2.8 Proportions and Similar Figures

I can find missing lengths in similar figures and use similar figures when measuring indirectly.

Same shape, but not necessarily same size

You can use proportions to find missing side lengths of similar figures.

The symbol ∼ means “is similar to”

Similar Figures

∆ABC ∼ ∆FGH

This means the triangles are similar.

In similar figures, corresponding angles are equal, and corresponding side lengths are proportional.◦ The order of the letters when making similar

figures is important

Example

If ∆ABC ∼ ∆DEF, what is the length of side DE?

Set up a proportion

Cross product 10(12) = 16(DE) 7.5 = DE

Practice

Using the same figure, find AC

You Try!

Use proportions to find measurement that you cannot find by measuring directly.

Create a proportion

x=25 feet

Indirect Measurement

Notice the map’s scale

You try!

ODDS ONLY P.134 #9-17, 23-31

Assignment