Question

Find the exact value of cos(7pi/12) using half-angle identities.

Answer 1

Answer:

I had no idea how to solve this on edge either. I ended up looking on you   tube and found this guy named Larry. He did it step by step in a short video!!! I will put it down below so you can watch it if you need help.

Step-by-step explanation:

The answer is B.√2-√6 over 4

video name on you tube:

cos 7pi/12 find the exact value of the trig function

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Answer 2

Using trigonometric half angle identities:
cos ( 7π/12 ) = $cos( \frac{ \frac{7 \pi }{6} }{2} ) = \\ =- \sqrt{ \frac{1+cos(7 \pi /6)}{2} } = \\= - \sqrt{ \frac{1- \sqrt{3}/2 }{2} } =- \sqrt{ \frac{2- \sqrt{3} }{4} } = \\ - \frac{ \sqrt{2- \sqrt{3} } }{2}$
... = -0.2588 ( correct )