# trig

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Find sin è/2 for sin è = 1/4 and è lies in Quadrant I.

• trig -

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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