1. cos4(theta)
2. cos 5pi/12
Need Help!! Thanks!!
What exactly do you have to do with Q1? The way you have left it does not suggest to either, prove, simplify or solve anything?
In Q2 apply the following formula
$\displaystyle cos(\tfrac{\theta}{2}) = \pm\sqrt{\frac{1-cos(\theta)}{2}}$
my solution is
$\displaystyle cos(\tfrac{5\pi}{12}) = \pm\sqrt{\frac{1-\frac{\sqrt{3}}{2}}{2}}$