Question

What is cos(7π5) ?

0.61
-0.61
0.31
-0.31

Answer 1

-0.31.

Explanation:

Cos (7π/5) is in the third quarter so the cosine is negative.

Cos 7π/5) = - cos (7π/5 - π)

= -cos 2π/5)

= -0.31.