AS Level Mathematics 9709 | Circular Measures 3 | Angle & Triangle Properties | Raja Shafqat — Transcript
Full transcript
- 0:08Assalam-o-Alaikum, beta. In the last
- 0:11class, we studied the geometrical
- 0:12properties of a circle. Today, we are
- 0:14discussing one more small point.
- 0:17Obviously, this point is also from
- 0:18O-Level math. Clear, beta? We call
- 0:21these angle properties. Basic angle
- 0:23properties. Now, what are these basic
- 0:24angle properties? There are three or
- 0:26four properties that we require. Now
- 0:28let's check them one by one. The first
- 0:30property—all these properties are
- 0:32from O-Level math. Well, whenever we
- 0:34talk about O-Level math, let's start
- 0:36with another property. Suppose this is
- 0:38a straight line. Okay? Suppose this is
- 0:40a straight line. Okay? And the angle
- 0:42given to you on this straight line, the
- 0:45name of this angle is angle A. Come on,
- 0:47the angle given to you, let's name this
- 0:50angle as angle A. Clear? If this is
- 0:53angle A, and I'll call this angle B.
- 0:56Let's name this angle as angle B. Okay?
- 0:59We named one angle as angle A and the
- 1:02other as angle B. Okay? Let me explain
- 1:04it again. Let me explain it again that
- 1:07if we have this angle A. If this angle
- 1:10is A, then this will be angle B. So,
- 1:12these two angles are called adjacent
- 1:14angles. Adjacent. So, what did we learn
- 1:17in O-Level math? Adjacent angles on a
- 1:19straight line are supplementary.
- 1:22Meaning their sum is always what? 180.
- 1:24So we learned in O-Level math that
- 1:25whatever angles are on a straight line,
- 1:27their sum is always what? 180. What do
- 1:30we call this in math language? In math
- 1:33language, we call it adjacent angles,
- 1:37adjacent angles, adjacent angles on a
- 1:41straight line. Adjacent angles on a
- 1:45straight line. Adjacent angles on a
- 1:49straight line are supplementary. This
- 1:52is a very basic condition that a child
- 1:54learns in very basic math. We call this
- 1:57condition that adjacent angles on a
- 1:58straight line are always supplementary.
- 2:01Supplementary means their sum should
- 2:03always be 180. If I tell you this angle
- 2:05is 60, then this angle will obviously
- 2:07be what? 120. So that the sum of these
- 2:10two is what? The sum of these two
- 2:12should be 180. The sum of these two
- 2:13should be what? 180. So it is a very
- 2:15basic condition. We call it adjacent
- 2:17angles on a straight line are
- 2:18supplementary. Supplementary means
- 2:20their sum should always be what? 180.
- 2:23Clear? We used to study one more
- 2:25property in O-Level math. We used to
- 2:28call it vertically opposite angles.
- 2:30Vertically opposite angles. Look, we
- 2:31used to show this like this too. Then I
- 2:33will plot its diagram and show you. We
- 2:36studied in O-Level Math that vertically
- 2:39opposite angles are equal. Vertically
- 2:43opposite angles are equal. Okay, now
- 2:47what was this property? Look, it's a
- 2:50small property. By the way, this is
- 2:52Class 9 Math. Suppose you have a
- 2:54straight line here. Okay? A straight
- 2:56line. I plotted another line on the
- 2:58straight line that is intersecting it.
- 3:00If I tell you, hey, this angle is angle
- 3:03C. Let me label it for a minute. This
- 3:06angle is your angle C. And let me label
- 3:08this angle. This angle is your angle D.
- 3:11Okay? One I labeled C, one I labeled D.
- 3:14And if I label this angle as angle B,
- 3:16okay, there you go, I labeled this
- 3:18angle. B and I labeled this angle as A.
- 3:22So what did we learn in O-Level Math?
- 3:24In O-Level Math, we learned that if
- 3:26this angle, let's say it's angle C,
- 3:28then angle C equals what angle? It is
- 3:30D. We used to say in O-Level Math that
- 3:33angle C = angle D and we used to say
- 3:35angle B = angle A. Let's see a simple
- 3:38proof for this for a minute. If this
- 3:41angle is 60, then obviously this angle
- 3:43on the straight line will be 180-60 =
- 3:44120, which we studied in the previous
- 3:46question. If this is 60, then this is
- 3:48120, so then this is also a straight
- 3:50line. If this is 120, then this will
- 3:52also be 60. And then this is also a
- 3:54straight line. If this is 60, then this
- 3:56will be 120. So technically, these two
- 3:59angles became? The same. And
- 4:00technically, these two angles became?
- 4:02The same. So basically, vertically
- 4:05opposite angles were derived from
- 4:07adjacent angles. Derived from adjacent
- 4:11angles. So these two angles will be
- 4:13equal, C and D, and these two angles
- 4:15will be equal, A and B. So we call
- 4:17these angles vertically opposite angles
- 4:19. Vertically opposite angles. We used
- 4:21to call these X-shape angles in O-Level
- 4:23Math too. Meaning these two angles are
- 4:25equal and these two angles are equal.
- 4:27So we used to call these X-shape angles
- 4:30in O-Level Math too. Used to call them
- 4:34X-shape angles. So this is also Class 9
- 4:37Math, basic adjacent angles on a
- 4:39straight line, meaning those angles
- 4:41which are on a straight line, both are
- 4:43equal angles. Both are next to each
- 4:45other. So their sum is always 180. And
- 4:47the second property was O-Level math's
- 4:49vertically opposite angles. Vertically
- 4:51opposite angles. Condition number three
- 4:54. Now we will study two things here.
- 4:57Condition number three was called
- 4:59alternate angles and corresponding
- 5:01angles in O-Level math. Alternate and
- 5:03corresponding. Okay? We are studying
- 5:05two more properties. In math
- 5:07terminology, we also call these
- 5:10properties angles formed by parallel
- 5:13lines. In math, we also call them
- 5:17angles formed by parallel lines. Angles
- 5:22formed by parallel lines. We also
- 5:24studied this in O-Level math. Obviously
- 5:26, all these conditions are from O-Level
- 5:27math. Angles formed by parallel lines.
- 5:31Look at how. Suppose you have this line
- 5:34. And this is another line. You see,
- 5:38these two lines are parallel. I drew
- 5:40these two lines parallel. Okay? I drew
- 5:43these two lines parallel. Here, I drew
- 5:45both lines parallel. Let's copy these
- 5:48two lines here. Wait a minute. Here.
- 5:51Let's get some more space. These two
- 5:53lines are parallel. Now suppose this
- 5:55line is cutting these two lines. Okay?
- 5:58Okay? Like this, I randomly drew a line
- 6:00that is cutting both these lines. It is
- 6:02cutting both these lines. Now look, if
- 6:04I tell you this angle is A, then you
- 6:05would say this angle is also the same.
- 6:07Let's name it A. Let's name this one C.
- 6:09So according to the previous condition,
- 6:12these two angles are equal. According
- 6:15to the previous condition. Clear?
- 6:16According to the previous condition. If
- 6:18I tell you this angle is D, then you
- 6:20would say this angle is also D. Let's
- 6:22name it B. Let's name this one D. So
- 6:24that means these two angles are equal
- 6:26according to the previous condition.
- 6:29These two angles are equal according to
- 6:31the previous condition. Clear, dear?
- 6:33Okay. So these two were equal by
- 6:35vertically opposite. These two were
- 6:36equal by vertically opposite. If this
- 6:38was 60, we know this is also 60. If
- 6:40this was 120, we know what this will be
- 6:42? This will also be 120. Okay, now I am
- 6:44telling you something new. Now suppose
- 6:47I am naming this angle E. I named this
- 6:50angle E. I named this angle F. Let's
- 6:53just mark it randomly. I named this
- 6:56angle F. I named this angle G and this
- 6:59angle H. Here is G and here is H. G and
- 7:02H. Okay, so now we have studied two
- 7:05conditions. Now look, the line
- 7:07intersecting is intersecting these two
- 7:09parallel lines. That is why, what is
- 7:11the condition? Angles formed by
- 7:13parallel lines. So, A and C were equal.
- 7:16B and D were equal. Similarly, E and F
- 7:18will be equal. Will G and H also be?
- 7:19They will be equal. So now look at the
- 7:22first condition; if this is 60, then
- 7:24obviously this is also 60, clear kiddo?
- 7:27Now we used to study a condition in O
- 7:29Level Maths. Look here, the Z shape
- 7:31formed here, there it is. So if I say,
- 7:34what is angle C? If this is 60, then
- 7:36this will also be 60. So we kept saying
- 7:39that angle C and E are both equal.
- 7:41Because what shape was formed here? A Z
- 7:43shape was formed. So we kept calling
- 7:45these alternate angles. In O Level
- 7:48Maths, we kept calling them alternate
- 7:50angles. Alternate angles, alternate
- 7:52angles are equal, and in O Level Maths
- 7:54we also used to call it this. There was
- 7:57a topic in O Level Maths called '
- 7:58Bearings'. Bearings, in math they also
- 8:01called this 'Z shape angles', 'Z shape
- 8:03angles'. So look, what was formed here?
- 8:06A Z shape was formed. So if this is C,
- 8:08then C and E will both be what? The
- 8:10same. What will C and E both be? The
- 8:13same. Clear kiddo? I can also read it
- 8:15like this. This Z shape is also formed
- 8:17this way, that if this is D, then D and
- 8:19G will also both be equal. So that
- 8:21means angle C and E will both be equal.
- 8:24Angle C = Angle E, so then I can also
- 8:26say, look, a Z shape is also being
- 8:29formed here. Here it is, so angle D and
- 8:31angle G will both be what? The same.
- 8:33Angle D = Angle G, so in O Level Maths,
- 8:36we used to call these two angles
- 8:38alternate angles. We used to call them
- 8:41Z shape angles. Alternate angles. Look
- 8:43again. If this is 60, then math says
- 8:45this is also 60. If this is 60, then
- 8:47math says this is also 120. This will
- 8:49also be 120. So if this is 60, then
- 8:51math says this will also be 60. If this
- 8:54is 60, then this will also be 60. If
- 8:56this is 120, then this will also be 120
- 8:59. Clear, kid? So we used to call these
- 9:01alternate angles. Alternate, alternate
- 9:04Z-shape angles. Alternate angles,
- 9:06meaning look, these two lines are
- 9:08parallel. This Z-shape angle is formed.
- 9:10If you look at it this way, these two
- 9:11lines are also parallel. So, these two
- 9:13angles will also be what? The same.
- 9:15Then we used to use another word.
- 9:17Corresponding angles are equal.
- 9:18Corresponding angles. We heard another
- 9:22word in O-level math; that word was
- 9:24corresponding angles. We used to hear
- 9:27another term, corresponding angles are
- 9:28equal. Just like alternate angles are
- 9:30equal. Corresponding angles. For
- 9:32corresponding angles, we used a word in
- 9:35math. That word, that sign was F-shape
- 9:37angles. F-shape. Note one thing. These
- 9:40two lines are parallel. Do you see the
- 9:42arrow sign? It's parallel. We learned
- 9:44that if this is 60, then this is 120.
- 9:47Similarly, if this is 60 and 120, then
- 9:49this was also 60 and 120. So, will
- 9:52angle A and angle E also be...The same?
- 9:55Angle, angle, I am repeating it again.
- 9:57This is an F-shape angle. So angle A
- 9:58and angle E will be equal. And angle D
- 10:00and angle H will also be equal. So I
- 10:02can say that angle A is equal to angle
- 10:05E. And I can also say that angle D is
- 10:08equal to angle H. So we used to call
- 10:11these angles corresponding angles.
- 10:14Corresponding, so we kept saying that
- 10:16corresponding angles are equal.
- 10:18Corresponding angles are equal. In math
- 10:20, we also called them F-shape angles.
- 10:22In math, we also used to call them
- 10:24F-shape angles. Look again. If this is
- 10:2660, then this will also be 60. If this
- 10:28is 120, then obviously this will also
- 10:30be 120. So this same situation will
- 10:32transfer below too. This is 60. If this
- 10:35was 60, then this is also 60. If this
- 10:38is 60, then this is also 60. If this is
- 10:40120, then this is also 120. Clear, kid?
- 10:43This is also 120. So we used to call
- 10:45these angles corresponding angles and
- 10:46alternate angles. Where are
- 10:48corresponding and alternate angles
- 10:49formed? Between parallel lines. Between
- 10:52parallel lines. Then we also used to
- 10:54study one more thing. Interior angles
- 10:56are supplementary. Then we used to
- 10:58study another condition. What was the
- 10:59name of that condition? The name of
- 11:02that condition was interior angles are
- 11:04supplementary. Interior angles are
- 11:08supplementary. Supplementary. Well,
- 11:12look, now let's see the proof for this
- 11:13too. Supplementary means their sum will
- 11:16be what? It will be 180. In math, this
- 11:19was also called C-shape angles. Or in
- 11:22math, this was also called U-shaped
- 11:25angles. C-shaped angles or U-shaped
- 11:27angles. C-shape or U-shape. We keep
- 11:30calling it C-shape or U-shape. Look how
- 11:33? Look, these two lines are parallel.
- 11:35Two minutes ago, I gave an example that
- 11:37if this is 60, then this will also be
- 11:3960. If this is 120, then obviously this
- 11:41will also be 120. This will also be 60.
- 11:44This will also be 60. This will also be
- 11:47120. This will also be 120. So you see
- 11:49that this 120 and this 60, what is
- 11:51their sum? This is a C-shaped angle.
- 11:53Look, this is a C-shaped angle. Here it
- 11:56is. So that means what will be the sum
- 11:58of E and D? 180. So we used to say in
- 12:01O-Level math that angle E and angle D,
- 12:04angle D and angle E, what will be their
- 12:07sum? It will be 180. So what will we
- 12:09call these two angles? How are these
- 12:10two angles? Supplementary. Meaning this
- 12:12is 120. This is 60. Look, what is the
- 12:14sum of both? Similarly, I can also say
- 12:16what is the sum of C and G? The sum of
- 12:19C and G is also 180. So I can also say
- 12:22that angle C and angle G, what is the
- 12:25sum of both? 180. What is the sum of
- 12:28both of these too? 180. Clear, dear? So
- 12:31we learned today that this angle and
- 12:32this angle are both equal. A and E,
- 12:34both these angles are equal. A and E,
- 12:36so can we say why they are equal?
- 12:38Corresponding. Angle D and angle H are
- 12:40also equal. Why can we say that?
- 12:42Corresponding. Then look, we learned
- 12:44about interior angles, the sum of D and
- 12:47E is 180. Then we studied again that
- 12:49these two lines are parallel. The sum
- 12:51of C and G is 180. So we studied four
- 12:53conditions. Number one, what is the
- 12:55angle on a straight line always? 180.
- 12:58Angle on a straight line, meaning
- 13:00adjacent angles are supplementary. Then
- 13:02we studied vertically opposite angles.
- 13:03C and D are equal. B and A are equal.
- 13:06Vertically opposite angles. Then we
- 13:08studied alternate angles, Z-shaped
- 13:10angles. C and E are both equal. Then we
- 13:13learned that these are also alternate
- 13:14angles. D and G are both equal. This
- 13:17became an alternate angle. Then we
- 13:19studied corresponding angles. Angle A
- 13:20and E are both equal. Then we learned
- 13:23that angle D and H are both equal.
- 13:25Angle B and F are both equal. Angle C
- 13:28and, sorry, angle B and G are both
- 13:31equal. Angle C and angle F are both
- 13:33equal. Clear? So what kind of angles
- 13:35are these? Corresponding angles. Then
- 13:37we studied, what is the sum of D and E?
- 13:39180. Because what shape is being formed
- 13:41here? C shape. C shape or U shape. Then
- 13:44we studied what the sum of C and G
- 13:46would be? This will also be 180.
- 13:47Because what shape is being formed here
- 13:49as well? C shape. Okay? C shape or U
- 13:53shape. Let me explain again. This is
- 13:55called a C shape or U shape. Here you
- 13:57go, C shape or U shape. C or U shape.
- 14:01We studied all these conditions. In O
- 14:03Level Math. In O Level Math. I am
- 14:05telling you one more small property.
- 14:07Then we will start further. So all
- 14:09these are adjacent angles, vertically
- 14:11opposite angles, alternate angles,
- 14:13corresponding angles, interior angles.
- 14:16So basically, we studied five points
- 14:18here. Basically, we studied five points
- 14:21here. Look, in the same way. Now there
- 14:24are some properties of triangles as
- 14:25well. Angle properties of triangles. I
- 14:28am telling you a small sixth point.
- 14:30Let's read this. Angle properties of
- 14:32triangles. Take a look at this once.
- 14:34Then God willing, we will proceed
- 14:36further. Its name is angle properties
- 14:39of triangles. Angle properties of
- 14:42triangles. Okay? This is a small
- 14:45condition. Angle properties of
- 14:47triangles. Now let's see what needs to
- 14:48be done in this. First of all, if I
- 14:50tell you that, hey, this is a triangle.
- 14:52I just randomly sketched a triangle.
- 14:54Here you go, I sketched a triangle.
- 14:56This is also obviously all O Level Math
- 14:58. I sketched a triangle. Math says if
- 15:01you see this is your angle q. Note it.
- 15:04Name this angle anything. Suppose this
- 15:07angle is Q. Suppose this angle is A.
- 15:09Suppose this angle is B and this angle
- 15:11is C. Come on, here you go. Let's label
- 15:13it like this, suppose this is A.
- 15:15Suppose this is B. Suppose this is C
- 15:16and suppose this is...Q. Let's name it
- 15:18D instead of Q. Name it anything. Here
- 15:20you go, this is D. So what did we study
- 15:22in O Level Math? We studied a property
- 15:25in O Level Math that the exterior angle
- 15:27of a triangle. We studied in O Level
- 15:30Math that the exterior angle of a
- 15:32triangle is equal to the sum of
- 15:34interior opposite angles. Well, if any
- 15:37student has a doubt, I will prove it to
- 15:39you. Look how, if I say this is 60. If
- 15:42I say this is 60. You will say this
- 15:44angle is 120 because of angles on a
- 15:45straight line. This is 120. Then answer
- 15:48me one thing. So, if I look at this
- 15:51triangle, what should the sum of a + b
- 15:54+ 120 be? 180. So, when that subtracts
- 15:58over there, what do I find the answer
- 16:00for a + b is? 60. That means if this is
- 16:0360, then look at these two interior
- 16:06angles, which angle is this? Exterior,
- 16:09and this is its interior angle. The
- 16:11angle next to the exterior is called
- 16:12the interior angle. These two are
- 16:14adjacent angles. So, math says that
- 16:17this exterior angle is equal to the
- 16:19opposite interior angles. So, what
- 16:22property did we learn in O Level Math?
- 16:25We learned the property in O Level Math
- 16:28that the exterior angle of a triangle
- 16:31...we learned in O Level Math. The
- 16:36exterior angle of a triangle is equal
- 16:41to the sum of the interior opposite
- 16:45angles. The exterior angle of a
- 16:48triangle is equal to the sum of the
- 16:51interior opposite angles. Listen again.
- 16:54This is the exterior angle of the
- 16:56triangle. The outer angle. For a minute
- 16:58, let me assume. This is 60. If this is
- 17:0160, this is exterior. Then who is its
- 17:03interior? 120. Now we know that the
- 17:06angle sum in a triangle is always 180.
- 17:10So, if this 120 subtracts over there,
- 17:13the answer for a + b is 60. Meaning a +
- 17:16b will indirectly be equal to d. So,
- 17:20math says that any triangle's exterior
- 17:22angle is equal to its opposite interior
- 17:25angles. This is exterior, this is
- 17:29interior, and the two angles other than
- 17:32the interior are called interior
- 17:35opposite angles. Interior opposite
- 17:38angles. So, there is a property of a
- 17:40triangle that the exterior angle of a
- 17:41triangle is equal to the interior
- 17:43opposite angles. And one thing everyone
- 17:46already knows is when we talk about any
- 17:48triangle, what is the interior sum of
- 17:50the triangle? What is the sum of all
- 17:52the angles in a triangle? It is 180. We
- 17:54already know that in a quadrilateral
- 17:56the sum is 360 and in a triangle the
- 17:58sum is 180. We already know this. We
- 18:01already know this. So, what do we call
- 18:03this? These are the angle properties of
- 18:05a triangle. Okay, I am telling you one
- 18:07more small property. Okay? We also
- 18:10studied this previously in circle
- 18:11properties. So, I will repeat it once
- 18:14more so that you remember it. Whenever
- 18:16we talk about an isosceles triangle in
- 18:18math, look, here it is. If I tell you
- 18:21the triangle is isosceles. If these two
- 18:23sides are equal, then we know that its
- 18:25two base angles will also be equal.
- 18:27Clear, son? So we used to say that if,
- 18:30let's say, I name this triangle ABC,
- 18:33then what did we say? In O-Level maths,
- 18:36we used to say that angle B and angle C
- 18:38will both be the same. We have already
- 18:41studied this property. I explained the
- 18:43name of this triangle in the circle
- 18:45properties. So, what is the name of
- 18:47this property? This is an isosceles
- 18:49triangle. What is the name of this
- 18:52triangle? Isosceles triangle. We have
- 18:55already studied this thing. The name of
- 18:57the topic was circle properties. I
- 18:59explained there too that when a
- 19:01triangle is isosceles, its two sides
- 19:03are equal. So its base angles will be
- 19:05equal. So the most important property
- 19:07of an isosceles triangle is that when
- 19:09you drop a line in it, what does it do
- 19:12to the base? It bisects the base of the
- 19:14isosceles triangle. Clear, son? When
- 19:18you drop a line in an isosceles
- 19:19triangle, what does it always do to the
- 19:21base? It bisects it. This is a property
- 19:24of an isosceles triangle. Okay? Of an
- 19:27isosceles triangle. So I can say that
- 19:29in an isosceles triangle, AB and AC are
- 19:31both equal. If these two sides are
- 19:33equal, then its base angles will also
- 19:36be equal. If AB and AC are both equal,
- 19:38then maths says that angle B and angle
- 19:40C will also both be equal. Angle B and
- 19:43angle C will both be equal. We studied
- 19:45this property of an isosceles triangle.
- 19:47So when you drop a line in an isosceles
- 19:49triangle, what does it always do to the
- 19:51base? It bisects it. Bisects. And it
- 19:54also divides both these angles equally.
- 19:57I have already explained this property
- 19:59in circles. Meaning, if I tell you that
- 20:01this angle is alpha, you will say that
- 20:02this is also alpha. This is a property
- 20:04of an isosceles triangle. Meaning, this
- 20:06is its line of symmetry. This can fold
- 20:08onto this, and this can fold onto this.
- 20:11Okay, son? Look at another triangle.
- 20:13Equilateral triangle. We also studied
- 20:15this in O-Level maths. Look at this one
- 20:16too, for once. Because why are we
- 20:17studying all these things? Because
- 20:19these are all required. They will be
- 20:20used in this. So the name of this
- 20:23triangle is an equilateral triangle.
- 20:27Equilateral triangle. Because we have
- 20:30already studied the right-angled
- 20:31triangle. The name of this point is an
- 20:33equilateral triangle. Well, we also
- 20:35studied in O-Level maths that any
- 20:36triangle whose three sides are equal is
- 20:38called an equilateral triangle in maths
- 20:40. Okay? What do we call it in maths?
- 20:42Let's draw a triangle. Suppose this is
- 20:45a triangle and all three sides of this
- 20:47triangle are equal. Suppose we name
- 20:49this triangle, let's name it. I have
- 20:53named the triangle ABC, here it is. I
- 20:55have named this triangle A, B, C. We
- 20:57have named this triangle A, B and C. So
- 21:00if the triangle is equilateral, then
- 21:02equilateral means what will its three
- 21:05sides be? They will be equal. So what
- 21:07did we learn in O-Level Math that when
- 21:09we talk about equilateral, an
- 21:10equilateral is also called a regular
- 21:12polygon. So that means if this is angle
- 21:14B, this is angle C, and this is angle A
- 21:15, then we know these three angles will
- 21:17be equal. So what did we learn in
- 21:19O-Level Math that if a triangle is
- 21:21equilateral, it means its three sides
- 21:23are equal. Meaning all three of its
- 21:25sides are equal. So then we learned in
- 21:27O-Level Math that its three angles will
- 21:29also be equal. Angle A, angle B, angle
- 21:32C, and we know we can say that all
- 21:35three angles will be the same, and what
- 21:37will all three angles be? 60. Because
- 21:41what we did was divide the angle sum
- 21:43equally. So in two or three questions
- 21:45in past papers, you will also find
- 21:47equilateral triangles. You will also
- 21:49find isosceles triangles and also this
- 21:51property that the exterior angle of a
- 21:53triangle is equal to the sum of
- 21:55interior opposite angles. And we all
- 21:58know this fact that in any triangle,
- 21:59what is the sum of the angles always?
- 22:02The sum of the angles is always 180. We
- 22:05all already know this. Clear, kid? So
- 22:07we haven't learned anything new yet. So
- 22:09this point we studied today is called
- 22:11geometrical properties, or let's call
- 22:13them angle properties. Angle properties
- 22:16. And we studied two things in this
- 22:19today. Adjacent, vertically opposite,
- 22:22alternate, corresponding, and interior.
- 22:26We studied these five properties. Then
- 22:28I told you about triangles. The
- 22:30triangle property that the exterior
- 22:31angle of a triangle is equal to the sum
- 22:33of the interior opposite angles. I told
- 22:35you about the isosceles property. Sides
- 22:37equal, base angles equal. When we drop
- 22:39a line, what will it do to the base?
- 22:41Bisect. We can also say that an
- 22:43equilateral triangle is a pair of three
- 22:45equal sides. I can say it that way too.
- 22:48These two sides are also equal to each
- 22:50other. These two sides are also equal.
- 22:52So technically, three pairs have been
- 22:54formed. This and this are equal. One,
- 22:56this and this equal, two, this and this
- 22:58equal, three, so technically
- 23:00equilateral means all sides are equal.
- 23:03So what happens in an equilateral
- 23:04triangle? There are three sides. There
- 23:07are three pairs of two equal sides.
- 23:09Three pairs of equal sides. Clear, dear
- 23:11? Alright, let's start the next point.
- 23:14This is mensuration. The mensuration
- 23:17related to circles that we studied in O
- 23:19Level Maths. That mensuration is also
- 23:21required for this topic. There is one
- 23:24more point after this. Then finally we
- 23:26will start our chapter. Mensuration.
- 23:28Let's start from absolute zero.
- 23:30Whatever mensuration related to circles
- 23:33we studied in O Level Maths, we need
- 23:35all of it. Number one, first of all,
- 23:38let's start with the circle in the
- 23:39circle family. We are starting the
- 23:42circle family with the circle itself.
- 23:45Now we need a bit of mensuration. What
- 23:47did we study in O Level Maths? We
- 23:49studied in O Level Maths, obviously,
- 23:51that this is a circle. Clear? We
- 23:54studied in O Level Maths that this is a
- 23:56circle. Alright? In the next class,
- 23:58InshaAllah, we will continue from here,
- 24:00dear. Okay?
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