Geometry covers angles, triangles, polygons, circle theorems, and similar and congruent shapes.
Angles on a straight line sum to $180°$; angles round a point to $360°$. Interior angles of a polygon sum to $(n-2)\times 180°$; exterior angles always sum to $360°$. The angle in a semicircle is $90°$.
Remember
- Interior sum $=(n-2)\times180°$ · Exterior sum $=360°$.
- Angle in a semicircle $= 90°$.