Calculating the area of a TRIGLE AN

If you can find the area of a square or rectangle, you can easily use this information to find the area of a triangle The area of a square or rectangle is the length multiplied by the width (breadth). length width This can be written as area = l x w

To calculate the area of this rectangle…….. Multiply the length……By the width 17cm 5cm 17 x 5 =85 So the area is 85 cm 2

A square or rectangle can be divided into 2 triangles

If you know how to calculate the area of a rectangle or square, and you know that a triangle is half of this shape, then you can work out that the area of a triangle must be….. Half the area of a rectangle or square Area of a rectangle = length (l) x width (w) Area of a triangle = ½ length (l) x width (w) Area of a triangle = ½l x w

Have a go at these Length 22 cm Width 8cm Area = ½ l x w l x w = 22 x 8 =176 ½ x 176 =88 Area is 88cm 2

Length 16 cm Width 6cm Area = ½ l x w l x w = 16 x 6 =96 ½ x 96 =48 Area is 48cm 2

Length 9 cm Width 9cm Area = ½ l x w l x w = 9 x 9 =81 ½ x 81 =40.5 Area is 40.5cm 2

Length 13m Width 4m Area = ½ l x w l x w = 13 x 4 =52 ½ x 52 =26 Area is 26m 2 Watch those units !!!!!!!!!

Length 6cm Width 14cm Area = ½ l x w l x w = 6 x 14 =84 ½ x 84 =42 Area is 42cm 2

Length 23cm Width 18cm Area = ½ l x w l x w = 23 x 18 =414 ½ x 414 =207 Area is 207cm 2

Things to note Check you have recorded the correct units in your answer Make sure you have halved the answer to your multiplication When finding the area of a triangle, the width is sometimes referred to as the height

Does this work for different types of triangle, isosceles and equilateral? The area taken up by the triangle is half that of the rectangle it would make.

Look at these triangles. Calculate the area of the rectangle they would make 5cm 16cm Area = length x width = 16 x 5 =80 Area is 80cm 2

7cm 9cm Area = length x width = 9 x 7 =63 Area is 63cm 2

13cm 14cm Area = length x width = 14 x 13 =182 Area is 182cm 2

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