Head First 2D Geometry

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quadrilaterals

If you don’t like what you’re given, change it

True, geometry has lots of rules, but moving things around doesn’t mean you’re

breaking them. By moving the shapes you created in the parallelogram around,

you were able to form a rectangle. And you know that it has the same height and

same base width as the original parallelogram. So now…you know how to find

the area of a parallelogram!

Here’s a new parallelogram lawn you’ve been asked to mow. What

should you charge for mowing it?

Parallelogram Area = Base Width × Height

Look familiar? It’s the

same formula you’d use

to calculate the area

of a rectangle.

Width

Height

The dotted line shows

the shape of the

original parallelogram.

We moved the end triangle

to form a rectangle.

45 meters

16 meters

34 meters

246 Chapter 6

sharpen solution

Here’s a new parallelogram lawn you’ve been asked to mow. What

should you charge for mowing it?

Q:

What if I only have one pair

of opposite sides? Do I still have a

parallelogram?

A: No. In order for a shape to be a

parallelogram, both pairs of opposite sides

must be parallel. If you only have one pair

of opposite parallel sides, your shape isn’t a

parallelogram.

Q:

Can I still use the same formula

for finding the area for that shape?

A: This formula is specific to

parallelograms. ...