SOLUTION: Please help me solve this equation use a double angle formulas to find the exact value of cos2u when sinu=3/5, where pi/2<u<pi

Question 690368: Please help me solve this equation
use a double angle formulas to find the exact value of cos2u when sinu=3/5, where pi/2
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
use a double angle formulas to find the exact value of cos2u when sinu=3/5, where pi/2 ..
cos2u=1-2sin^u
=1-2*(3/5)^2
=1-18/25
=7/25
..
calculator check:
u=sin^-1(3/5)≈2.498 (in quadrant II)
2u≈4.9961 (in quadrant IV where cos>0)
cos2u=cos(4.9961)≈0.2799..
7/25=0.28
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