Answer
10a. $0.809$
10b. $0.809$
Work Step by Step
$\frac{\pi}{5}$ is not part of the unit circle of trignometric values, so a calculator is necessary for 10a and 10b
10a. $cos(\frac{\pi}{5})$ = 0.809
10b. $cos(\frac{-\pi}{5})$ is in the 4th quadrant, which is positive for cosine.
$= 0.809$
