SOLUTION: find cos x , if tan 2x=-3/4

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Question 839181: find cos x , if tan 2x=-3/4
Answer by lwsshak3(11628) About Me  (Show Source):
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find cos x , if tan 2x=-3/4
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cos(2x)=-4/5

calculator check:
tan 2x=-3/4
2x≈143.13˚(in quadrant II in which tan<0)
x≈71.56˚
..
cosx as calculated=√10/10
x≈71.56˚