Question

Trig, Coterminal angles... Which of the following are coterminal with -pi/4 ... (a) 7pi/4 (b)3pi/4 (c)-5pi/4) (d)-9pi/4 (e) pi/4

Answer 1

Correct answers are a) and d)

$\alpha=- \frac{\pi}{4}$

Coterminal angles: $\alpha+k\pi,\,k\in Z$

$- \frac{\pi}{4}+2\pi=- \frac{\pi}{4}+ \frac{8\pi}{4} = \frac{7\pi}{4} \\ \\- \frac{\pi}{4}-2\pi=- \frac{\pi}{4}- \frac{8\pi}{4} = -\frac{9\pi}{4}$