This document provides reminders of several geometric rules for determining unknown angle measures, including that angles in a straight line equal 180 degrees, angles in a triangle equal 180 degrees, interior angles of a quadrilateral equal 360 degrees, vertically opposite angles are equal, corresponding angles are equal, and alternate angles are equal. Examples are given applying each rule to solve for unknown angle measures.

2. Triangles, Straight and Parallel Lines What size is angle A ? Angles in a Straight Line Equal 180 ° A 45 °

3. 45 ° What size is angle B ? B Angles in a Triangle Equal 180 ° Triangles, Straight and Parallel Lines

4. 90 ° What size is angle B ? B Triangles, Straight and Parallel Lines 90 ° 90 ° Angles in a Q uadrilateral Equal 360 °

5. What size is angle C ? 40 ° Vertically Opposite Angles are Equal Triangles, Straight and Parallel Lines C

6. D What size is angle D ? 140 ° Interior Angles Sum to 180 ° Triangles, Straight and Parallel Lines

7. 40 ° What size is angle E ? E Corresponding Angles are Equal Triangles, Straight and Parallel Lines

8. 140° F What Size is angle F ? Alternate Angles are Equal Triangles, Straight and Parallel Lines