Final answer:
Another way to state the relationship between sine and cosine is that the sine and cosine of complementary angles are equal. This is because sine and cosine are co-functions of each other in the context of right angled triangles.
Step-by-step explanation:
The relationship between sine & cosine can be another way to understand the relationship between angles and the sides of right angled triangles. Specifically, the answer to the question is (c) The sine and cosine of complementary angles are equal. This is because sine and cosine are co-functions, such that for any angle θ, sin(θ) = cos(90° - θ). We can understand this by looking at the definitions on the unit circle, or by using right triangles. For instance, if θ is an angle in a right triangle, with 'x' as the adjacent side, 'y' as the opposite side, and 'h' as the hypotenuse, then cos(θ) = x/h and sin(θ) = y/h. If we take the complementary angle (90° - θ), the roles of 'x' and 'y' as adjacent and opposite sides are switched, and hence sin(90° - θ) = cos(θ).