Back to Unit 9

Area of a Triangle



Consider a triangle with base length b and height h.
The area of the triangle is 1/2 ( b  h).

To picture this, we could take a second triangle identical to the first, then rotate it and "paste" it to the first triangle as pictured below:


The figure formed is a parallelogram with base length b and height h, and has area b h.
This area is twice that of the triangle, so the triangle has area 1/2(b 


What is the area of the triangle below having a base of length 5.2 and a height of 4.2?
The area of a triangle is half the product of its base and height, which is 1/2 5.2  4.2 = 2.6  4.2 = 10.92.