A. -cos 2pi/3

B. cos 2pi/3

C. cos 6pi/3

D. -cos 5pi/3

E. cos 4pi/3

answer is A why????

another ....

for all y, the cos y is equal to which of the following?

A. siny

B. cos(y + pi)

C. sin (-y)

D. sin y+ cos y

E. cos (-y)

answer is E why??

these problems really get me. i know they're not hard, it's just when i look at them, i'm not even sure about what trig info i should be using to solve them. any suggestions about which identities, etc. i should know for the QR section as well as explanations to these problems would be fantastic! thank youu!