Question

Use a sum or difference formula to find the exact value of the given expression.
cos 5π/12

Answer 1

\[\frac{5\pi}{12}=\frac{\pi}{6}+\frac{\pi}{4}\]
or if it easier convert to degs then find the special sum

\[\frac{5\pi}{12} rad=\frac{5 \pi}{12} \cdot \frac{180 \deg}{\pi rad}= \frac{5(180)}{12} \deg=5(15) \deg=75 \deg \\ 75 \deg=30\deg+45 \deg \]

Answer 2

now you just have to use the cos sum identity

Answer 3

THANKS