Question

Find an exact value.
cos(-7pi/12)

Answer 1

Hint: \[Cos(-x)=cosx\]

\[Cos(7 pie/12) = Cos (pie - 5pie/12) = -\cos(5pie/12)\]

\[Cos(5pie/12) = \cos(75) = \cos(45+30)\]

\[Cos(x+y) = cosx.cosy+sinx.siny\]

Answer 2

thank you