SOLUTION: Use a double-angle formula to find the exact value of cos(2u) when sin(u)=8/17, where pi/2< u < pi.

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Question 937535: Use a double-angle formula to find the exact value of cos(2u) when sin(u)=8/17, where pi/2< u < pi.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
when sin(u)=8/17 the cosu = 15/17 17%5E2+-+8%5E2+=+225
.....
cos(2u) = 2cos^2u -1 = 2(15/17)^2 - 1