Head First 2D Geometry

two trapezoids make a parallelogram

264 Chapter 6

Here are two congruent trapezoids. Draw them together so that

they form a single parallelogram.

Calculate trapezoid area using

base length and height

So what we’ve discovered is that, like with the other

shapes you’ve encountered so far, there’s a shortcut

we can take if we want to find the area of a trapezoid.

All we need to do is add together the upper and lower

base lengths, multiply by the height, and then divide

by two.

Trapezoid Area = height (base 1 + base 2)

2

Parallelogram width = trapezoid lower base + trapezoid upper base

The parallelogram is made up of two trapezoids. This means that the area of each trapezoid

must be half that of the parallelogram, and we know that the area of a parallelogram is equal to

height x width.

What’s the width of the parallelogram?

The trapezoid upper and lower bases added together.

What’s the height of the parallelogram?

The trapezoid height

What ideas do you have about how to calculate the area of a trapezoid?

Spin one of the

trapezoids 180˚ and

you can fit them

both together to

form a parallelogram.

=

trapezoid height

Parallelogram height

you are here 4 265

quadrilaterals

What’s the charge for maintaining the trapezoid lawn? Thankfully, Ed went back and collected

some extra measurements ...