MathLines and AnglesHigh frequency
SAT Math: Apply the triangle angle sum theorem (angles sum to 180°)
24+ practice questions in Praczo
What you need to know
The concept, explained
- 1
The three interior angles of any triangle sum to 180°.
- 2
Use this to find a missing angle: if two angles are known, subtract from 180°.
- 3
For isosceles triangles, two base angles are equal; for equilateral, all three are 60°.
- 4
The exterior angle of a triangle equals the sum of the two non-adjacent interior angles.
Common mistakes
- ✗ Assuming a right angle in a triangle without evidence.
- ✗ Forgetting that the angles must sum to exactly 180°, not 90° or 360°.
Try a sample question
SAT-style practice
In triangle ABC, angle A measures 40° and angle B measures 75°. What is the measure of angle C?
24+ questions ready to practice
Ready to master this concept?
Praczo tracks your mastery on all 183 SAT concepts — not just broad topics. One sample question is a start; drilling to mastery is how scores move.
3-day free trial — no credit card required