Question

Which of the following statements is true? a. sin 18° = cos 72° b. sin 55° = cos 55° c. sin 72° = cos 18° d. Both a and c. Please select the best answer from the choices provided A B C D

Answer 1

D. Both a and c are true.

Explanation:

a . sin 18 = cos (90 - 18) = cos 72 so a is True.

b. this is not true.

c. sin 72 = cos(90 - 72) = cos 18, so c is true.

Answer 2

D

generally,

`\sin( \alpha ) = \cos(90 - \alpha )`

you can visualize this by drawing a right triangle with acute angles a and 90-a