SOLUTION: please help me solve this trig question: 2cos2 theta+ cos theta= 1 on the interval 0_< theta< 2 pi find exact answers

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Question 870543: please help me solve this trig question: 2cos2 theta+ cos theta= 1 on the interval 0_< theta< 2 pi find exact answers
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Let u=cos%28theta%29.
2u%5E2%2Bu-1=0
%28u%2B1%29%282u-1%29=0
Two solutions:
u%2B1=0
u=-1
+cos%28theta%29=-1
theta=pi
and
2u-1=0
2u=1
u=1%2F2
cos%28theta%29=1%2F2
theta=pi%2F3 and theta=%285%2F3%29pi