SOLUTION: Please help me solve this equation for u: cos2u-7cosu+7=0 with [0,2pi) as a restriction.

SOLUTION: Please help me solve this equation for u: cos2u-7cosu+7=0 with [0,2pi) as a restriction.

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Question 775868: Please help me solve this equation for u: cos2u-7cosu+7=0 with [0,2pi) as a restriction.
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
solve this equation for u: cos2u-7cosu+7=0 with [0,2pi) as a restriction.
***

solve for cos(u) by quadratic formula:

a=2, b=-7, c=-8
cos(u)≈4.41(reject, (-1 < cos(u) < 1)
or
cos(u)≈-0.9075
u=0.4335, 3.575 (in Q3 and Q4 where cos<0)

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