**Question from Joy:**

We are in Geometry 3 rd edition. Chapter 14 lesson 2 number 22-23. Page 582.

How do you get 108?

The answer in key says 3 x 180/5? Why? I think I missed something important yet simple. I was thinking divide 360/5. What an I doing wrong? Thanks!

**Answer from Dr. Callahan:**

I have to admit – I could not find this in the book. I think it SHOULD be there – but could not find it.

The answer is the a triagle has interior angles that add up to 180 (we know that – right)

So each time we add a side (triangle to square) we add 180.

See here https://www.mathsisfun.com/geometry/interior-angles-polygons.html

So in #22, he is saying we have 180 3 times (triangle plus 2 sides adding 2 more 180s) as the total angles and then dived by the number of sides to get 108.

Again – I do not see this in the book.

Hope this helps

dwc