SATElite (750+)Frequency: 1 - 2 questions
Similar Triangles & Complementary Angle Trig (sin x = cos(90 - x))
A recurring SAT favorite is the complementary angle identity: sin(x°) = cos(90° - x°). In a right triangle, the acute angles sum to 90°. If sin(A) = cos(B), then A + B = 90°.
Core Formula & Concept Cheat Sheet
1sin(x) = cos(90° - x) and cos(x) = sin(90° - x)
2If sin(2x - 10) = cos(3x + 20), then (2x - 10) + (3x + 20) = 90°
3In similar triangles, corresponding trig ratios are equal.
The 700+ Score Trap
Setting the arguments equal to each other instead of setting their sum equal to 90 degrees.
Test Your Mastery
Official Exam FormatLive Interactive Practice Drill
In a right triangle, acute angles A and B satisfy sin(3x + 5)° = cos(2x + 10)°. What is the value of x?
Frequently Asked Questions
Does this rule work in radians?
Yes! In radians, sin(x) = cos(π/2 - x), so the acute angles sum to π/2.