Angles on a straight line add up to $180°$; angles around a point add up to $360°$.
Complementary angles add to $90°$; vertically opposite angles are equal. Example: if one angle on a straight line is $110°$, the other is $180° - 110° = 70°$.
Remember
- Straight line $= 180°$ · Around a point $= 360°$.
- Complementary $= 90°$ · Vertically opposite angles are equal.