This problem is a checkpoint for finding angles in and areas of regular polygons. It will be referred to as Checkpoint $10$.  

1. What is the measure of each interior angle of a regular $20$-gon?

2. Each angle of a regular polygon measures $157.5º$. How many sides does this polygon have?

3. Find the area of a regular octagon with sides $5$ cm.

Check your answers by referring to the Checkpoint 10 materials located at the back of your book.

Ideally, at this point you are comfortable working with these types of problems and can solve them correctly. If you feel that you need more confidence when solving these types of problems, then review the Checkpoint $10$ materials and try the practice problems provided. From this point on, you will be expected to do problems like these correctly and with confidence.