Question

cos^2(5pi/12).
I know that is (1+ cos5pi /12) 2 , but am stuck after that

Answer 1

actually...
\[\Large \cos^2 (\frac{5\pi}{12}) \implies \left[\cos (\frac{5\pi}{12})\right]^2\]
i dont think those are the same...

Answer 2

i have to use the half angle formula

Answer 3

right, as \(\frac{5}{12}\) is half of \(\frac{5}{6}\) so use the half angle formula with \(\theta=\frac{5\pi}{6}\)

Answer 4

your mistake is in your post is that you need \(\theta =\frac{5\pi}{6}\) in the formula, not \(\frac{5\pi}{12}\)

Answer 5

i.e. it should be
\[\frac{1+\cos(\frac{5\pi}{6})}{2}\]

Answer 6

oh i see