The Area Of A Triangle.

1
The Area Of A Triangle.
Consider the right angled triangle below
What is the area of the triangle ?
Area ½ x 40 20cm2
What shape is the triangle half of ?
The formula for the area of a triangle is
Rectangle
Area ½ x Base x Height
What is the area of the rectangle?
A(tri) ½ x b x h
Area 8 x 5 40 cm2
2
Does the formula apply to all triangles ?
Can we make this triangle into a rectangle ?
Yes
The triangle is half the area of this rectangle
The areas marked A1 are equal.
The areas marked A2 are equal.
For all triangles A(tri) ½ x b x h
3
Calculate the areas of the triangles below
Example 1
Example 2
Solution.
Solution.
A(tri) ½ x b x h
A(tri) ½ x b x h
½ x 10 x 6
½ x 6.4 x 3.2
30cm2
10.24m2
4
Example 3.
Calculate the area of the shape below
Solution.
Divide the shape into parts
Area A1 A2
10
10
12
16-12 4
Area b x h 1/2 x b x h
Area 10 x 12 ½ x 4 x 10
Area 120 20
Area 140m2
5
What Goes In The Box ? 2
Find the area of the shapes below
40cm2
32.13m2
258m2