Posted by Steve on Wednesday, December 16, 2009 at 10:06pm.
I am going to use
cos 2A = 1 - 2sin^2 A
or
cos è = 1 - 2sin^2 (è/2)
so we first have to know cos è
make a diagram using sin è = 1/4
then cos è = √15/4
back in our equation...
√15/4 = 1 - 2sin^2 (è/2)
which solves to √[(4-√15)/8]
(I tested my answer on a calculator)
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