1. **Complementary Angles** A complementary angle pair sums to 90°. - Given a right angle (90°), split into two angles: $x$ and $90° - x$. - Example: If $x = 40°$, then the other angle is $90° - 40° = 50°$. 2. **Supplementary Angles** Supplementary angles sum to 180°. - On a straight line (180°), two angles $A$ and $B$ share a vertex. - If $A = 120°$, then $B = 180° - 120° = 60°$. 3. **Vertically Opposite Angles** When two lines cross, opposite angles are equal. - At intersection point $O$, angles opposite each other are equal. - If angle 1 is $70°$, its vertically opposite angle is also $70°$. 4. **Full Turn Angles** A full turn around a point is $360°$. - An arrow starting at a point on a circle and rotating fully back to start measures $360°$. These angle relationships help solve many geometry problems by using the sum properties and equality of angles.