Angles and Lines
Angle questions on the SAT come down to a few rules — straight lines sum to 180°, vertical angles match, and parallel lines cut by a transversal create predictable equal-or-supplementary angle pairs.
| Pair | When | Relationship |
|---|---|---|
| Vertical angles | Two lines cross | EQUAL |
| Linear pair (supplementary) | Two angles on a straight line | Sum = 180° |
| Complementary angles | Two angles together = right angle | Sum = 90° |
| Corresponding angles | Parallel + transversal, same position | EQUAL |
| Alternate interior angles | Parallel + transversal, between, opposite | EQUAL |
| Same-side interior | Parallel + transversal, between, same side | Sum = 180° |
| Polygon | Sides | Angle sum | Each angle (regular) |
|---|---|---|---|
| Triangle | 3 | 180° | 60° |
| Quadrilateral | 4 | 360° | 90° (square) |
| Pentagon | 5 | 540° | 108° |
| Hexagon | 6 | 720° | 120° |
| Octagon | 8 | 1080° | 135° |
Identify which rule applies (straight line, vertical angles, triangle sum, parallel-line rules, polygon sum). Chain rules together if needed to find the unknown angle.
The exterior angle of a triangle measures 130°. One of the non-adjacent interior angles is 70°. What is the other non-adjacent interior angle?
Worked examples
Common pitfalls
Key takeaways
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Checkpoint
10 questions on Lines, Angles, and Triangles, from our question bank. Score 70% or better across 10 answers to reach Silver and pass this step.