Question 828965: Find The value of cos2x if cotx=12/5, where pi < x <3pi/2
Answer by lwsshak3(11628)   (Show Source):
You can put this solution on YOUR website! Find The value of cos2x if cotx=12/5, where pi < x <3pi/2
cotx=12/5(working with a (5-12-13) reference right triangle in quadrant III in which sin<0, cos<0
sinx=-5/13
cosx=-12/13
..
cos2x=cos^2x-sin^2x=144/169-25/169=119/169
..
Calculator check:
cosx=-12/13 in quadrant III
x≈202.62
2x≈405.24˚
cos2x≈cos(405.24)≈0.7041..
Exact value as calculated=119/169≈0.7041..
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