2. The distance from any point on a circle to the center is a constant called the radius. The length of any line segment from a point on a circle to the center of the circle is a constant called the radius. All radii of a circle are the same length.

3. A B C

4. A B C

5. Alternate interior angles are equal. Vertical Angles are equal. Alternate exterior angles are equal. Corresponding angles are equal.

6. A B C CA

7. A B C

8. A B C B A

9. Proposition 4. SAS Congruence Theorem If two triangles have two sides and the angle included (formed) by the sides equal, then the triangles are congruent. Remember: things that are congruent are equal, in every respect.

10. Proposition 5. Base angles of an isosceles triangle are equal.

11. Proposition: Bisect a given angle.

12. Propostion 8. SSS Congruence Theorem If two triangles have all three sides equal, then the triangles are congruent. Remember: things that are congruent are equal, in every respect.