Chapter 1 of 10All chapters
Chapter 1 of 10
Angles
The rules that solve most diagrams.
The basics
Angles on a straight line add to 180 degrees and angles around a point add to 360. Vertically opposite angles, where two lines cross, are equal.
- Acute is under 90, right is 90, obtuse is between 90 and 180, reflex is over 180.
- Most diagram questions are these three rules used in sequence.
Parallel lines
A line crossing two parallels creates equal corresponding and alternate angles, and co-interior angles that add to 180. Spotting the Z, F and C shapes solves them quickly.