Question

Which of the following is NOT equivalent to cos 240° ?
(5 points)
Responses

A) cos 120°

A) cos 120°


B) −sin 150°

B) −sin 150°


C) −sin 210°

C) −sin 210°


D) sin 330°

D) sin 330°

Answer 1

cos 240° = cos(180°+60°) = −cos60° = −1/2.

Evaluate each option:
- A) cos120° = cos(180°−60°) = −cos60° = −1/2 → same
- B) −sin150° = −sin(180°−30°) = −sin30° = −1/2 → same
- C) −sin210° = −sin(180°+30°) = −(−sin30°) = +1/2 → not same
- D) sin330° = sin(360°−30°) = −sin30° = −1/2 → same

So the one NOT equivalent is C) −sin 210°.