Two angles are supplementary. If one angle measures 65°, what is the measure of the other angle?

Question

Accepted Answer

115°. Supplementary angles are two angles whose measures add up to 180°. If one angle is 65°, the other is 180° - 65° = 115°. Together they form a straight line (a straight angle of 180°).

"25°" (25°) would be the complement of 65°, not the supplement. Complementary angles add up to 90° (forming a right angle), while supplementary angles add up to 180° (forming a straight angle). This distinction is one of the most commonly tested concepts in basic geometry. "295°" (295°) equals 360° - 65°, which would be the reflex angle that, together with 65°, forms a complete rotation  -  this is not the definition of supplementary. "65°" (65°) would make the angles equal, but 65° + 65° = 130° ≠ 180°.

Key angle relationships to know for the CLEP exam include: complementary angles (sum to 90°), supplementary angles (sum to 180°), vertical angles (formed by two intersecting lines; they are always equal), and angles formed by parallel lines cut by a transversal (corresponding angles are equal, alternate interior angles are equal, co-interior/same-side interior angles are supplementary). Being able to quickly identify and apply these relationships is essential for solving geometry problems efficiently.

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