Hi! I can't prove that sq rt of (2 + sq rt of (2 + 2 cos x)) = 2sin(x/4). Thank you!

Question

Pls help! Oh, x is 270 degrees < x < 360 degrees

Answer 1

Let x = 120 degrees.

Then cos x = -0.5 and sin (x/4) = 0.5

 

Calculate left side; calculate right side (of your equation). They do not appear to be the same. 

 

Counterexample disproves the claim.

Answer 2

As written , they are not the same