SAT Math: Angle Relationships (Vertical, Supplementary, Parallel Lines)
31+ practice questions in Praczo
The concept, explained
- 1
Vertical angles are equal. They are formed by two intersecting lines and are across from each other.
- 2
Supplementary angles sum to 180°. A straight line forms a 180° angle.
- 3
Complementary angles sum to 90°.
- 4
When a transversal crosses parallel lines: alternate interior angles are equal, corresponding angles are equal, co-interior (same-side interior) angles are supplementary.
- 5
The exterior angle of a triangle equals the sum of the two non-adjacent interior angles.
- ✗ Confusing alternate interior angles (equal) with co-interior angles (supplementary).
- ✗ Forgetting to use the exterior angle theorem and instead solving the long way with all three interior angles.
SAT-style practice
Two parallel lines are cut by a transversal. One co-interior angle measures 65°. What is the measure of the other co-interior angle?
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