SAT Math: Identify complementary and supplementary angles
22+ practice questions in Praczo
The concept, explained
- 1
Complementary angles sum to 90°. Supplementary angles sum to 180°.
- 2
Memory trick: "C" comes before "S" in the alphabet and 90 comes before 180 — Complementary = 90, Supplementary = 180.
- 3
If one angle is x, the complement is 90 - x and the supplement is 180 - x. Set up a quick equation whenever a ratio or relation is given.
- 4
Angles that form a straight line are supplementary. Angles that form a right angle are complementary.
- 5
Complementary and supplementary angles don’t have to be adjacent — they just have to add to 90 or 180.
- ✗ Swapping the two definitions (complementary = 180, supplementary = 90).
- ✗ Assuming complementary/supplementary angles must share a side; the relationship is purely about the sum.
- ✗ Writing 90 + x instead of 90 - x for the complement.
SAT-style practice
The measure of angle A is 27° more than twice the measure of its complement. What is the measure of angle A, in degrees?
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