Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 5 - No. 23)
What is the relationship between the sine and cosine of an angle?
They are equal.
They are reciprocals.
They are complementary in right-angled triangles.
They are unrelated.
Explication
Sine and cosine are complementary angles (sin(x) = cos(90-x))