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00:00Hi kids, today we will learn more about triangles.
00:08So let's start.
00:12Parameter is the distance around the edges of a triangle.
00:18If we have to find the parameter of a triangle, we just add up the lengths of all the edges
00:25of a triangle.
00:29Like here is a triangle, with its sides A, B and C.
00:38So the parameter of this triangle will be A plus B plus C, that is sum of all the sides
00:49of a triangle.
00:53So the formula for finding the parameter of a triangle is A plus B plus C, where A, B,
01:05C are lengths of sides of the triangle.
01:11Let's take an example.
01:14Here we have a triangle, with the lengths of its sides mentioned.
01:21Now let's calculate its parameter.
01:26We know parameter is equal to A plus B plus C.
01:34Here A, B and C are lengths of sides of the triangle.
01:41Here A, B and C equals to 5, that is all sides measure 5 cm.
01:52So parameter is equal to 5 plus 5 plus 5 equals 15 cm.
02:02Now let's take another example.
02:08Here we have a scaling triangle, with length of all sides mentioned.
02:14Now let's calculate its parameter.
02:19We know parameter equals A plus B plus C, where A, B and C are lengths of sides of the
02:32triangle.
02:34And here the lengths of sides of the triangle are 3, 4 and 5.
02:41So parameter equals 3 plus 4 plus 5 equals 12.
02:49So here the parameter equals to 12 cm.
02:56Now let's take another example.
03:01Here is a triangle.
03:04Lengths of two sides of this triangle is mentioned.
03:10Parameter of this triangle is also mentioned.
03:15Can you calculate the length of its third side?
03:19Let's find it out.
03:22Let the third side be X cm.
03:29We can write it in the form of a mathematical equation, as 4 cm plus 5 cm plus X equals
03:4114 cm, that is 14 cm.
03:49Now let's solve this equation.
03:544 plus 5 we get 9, so 9 cm plus X equals 14 cm.
04:05And solving the equation, we get to know X equals 14 cm minus 9 cm, and so we get X equals
04:185 cm.
04:21So the third side of the triangle is 5 cm.
04:27So we got to know that we need to subtract the sum of two sides from the parameter of
04:34the triangle to get the length of third side of the triangle.
04:41Now let's take another example.
04:47Here we have a triangle, and its parameter is given.
04:52It is 22 cm.
04:56And length of two of its sides is given.
05:00It's 10 cm and 6 cm.
05:04And we have to find the length of the third side of this triangle.
05:10And we know length of the third side equals parameter minus sum of the other two sides.
05:20Here the sum of other two sides will be 10 cm plus 6 cm equals 16 cm.
05:32So the length of the third side equals parameter minus 16 cm, where parameter equals 22 cm.
05:46So the length of the third side is 6 cm.
05:51Kids, we need to know that in any triangle, the sum of the length of any two sides is
05:59always greater than the third side.
06:04Now we will be learning how to find the area of a triangle.
06:10Here we have a triangle.
06:12We have to find its area.
06:16For finding its area, we need two things, base, height.
06:26Base of triangle can be any side of the triangle.
06:30And height is measured at right angle to the base.
06:35That is, let any side of triangle be the base.
06:41And draw a perpendicular to it to get the height of the triangle, like this.
06:49An area is equal to base multiplied by height divided by 2.
06:58Now let's take an example.
07:01Here we have a triangle.
07:05Let's find its area.
07:08We know area equals base multiplied by height divided by 2.
07:17And base can be any side of triangle on which we draw a perpendicular.
07:24And here it's a right triangle.
07:28So already there is a perpendicular AB to the base BC.
07:35So the area of triangle ABC equals base multiplied by height divided by 2.
07:45And here length of the base is 3 centimeters.
07:50And length of height is 4 centimeters.
07:54So 3 multiplied by 4 divided by 2, 3 multiplied by 4 equals 12.
08:0312 divided by 2 equals 6 centimeters.
08:09So the area is 6 centimeters square.
08:15Remember, the unit of area is always centimeter square or meter square.
08:22That is always in square units.
08:26And we write it like this.
08:29Area of this triangle is 6 centimeters square.
08:36We can also find the area of triangle the other way.
08:41You can also take the perpendicular BC to the base AB.
08:48Let's find this way also.
08:51So area of triangle ABC equals base multiplied by height divided by 2.
09:01And here the base is 4 centimeters and height is 3 centimeters.
09:06So 4 multiplied by 3 divided by 2.
09:13So the area of triangle will be again 12 divided by 2 equals 6 centimeters square.
09:23So kids, any side of the triangle can be a base on which the perpendicular is drawn.
09:32Now let's find the area of another triangle.
09:38Here we have a triangle.
09:40We have to find its area.
09:43And we know area is base multiplied by height divided by 2.
09:49And here height is given.
09:52It is 12 centimeters.
09:54And base is also given, which is 20 centimeters.
10:00So area equals 12 multiplied by 20 divided by 2.
10:0812 multiplied by 20 equals 240.
10:15240 divided by 2, we get 120.
10:22So the area is 120 centimeters square.
10:30Now let's take another example.
10:33Here we have a triangle.
10:36We have to find its area.
10:39We know we can take any side as base.
10:43So let BC be the base.
10:46Now as it's not a right triangle, so we will have to draw a perpendicular to the base to
10:55find the area.
10:58So let's draw a perpendicular to the base BC.
11:03You can use a protractor to draw a perpendicular.
11:09Now here we have a perpendicular.
11:13Now let's measure the height of perpendicular using a scale.
11:20Measure the height of triangle, measuring the height of perpendicular up to the vertex
11:26opposite to base BC, that is vertex A. And height of the triangle is 5 centimeters.
11:37Now we can find the area.
11:40We know area is base multiplied by height divided by 2.
11:47Height is 5 centimeters.
11:50And the base is 14 centimeters.
11:5414 multiplied by 5, we get 70.
12:0070 divided by 2, we get 35.
12:05So area of triangle is 35 centimeters square.
12:12So kids, today we learned about triangles, how to find their perimeter and area.
12:21Now you may go ahead and take a quiz to learn more.
12:24Bye-bye.