Question

Which of the following statements is true?

Answer 1

D

Explanation:

If x° and y° are complementary angles, then x°+y°=90° and

`\sin x^(\circ)=\cos y^(\circ) \ [\text{Cofunctions rule}]`

Check all options:

A. 18°+72°=90°, so

`\sin 18^(\circ)=\cos 72^(\circ)\ [\text{true}]`

B. 55°+55°=110°, these angles are not complementary and

`\sin 55^(\circ)\\eq\cos 55^(\circ)\ [\text{false}]`

C. 72°+18°=90°, so

`\sin 72^(\circ)=\cos 18^(\circ)\ [\text{true}]`

D. Both A and C are true.