SOLUTION: 15 cos^2x+2cos x-1=0 [-2,2] (radian mode)

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Question 806724: 15 cos^2x+2cos x-1=0 [-2,2] (radian mode)
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
15 cos^2x+2cos x-1=0 [-2,2] (radian mode)
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15cos%5E2%28x%29%2B2cos%28x%29-1=0
(5cos(x)-1)(3cos(x)+1)=0
..
5cos(x)-1=0
cos(x)=1/5
x=1.37,4.91 (In quadrants I and IV where cos>0)
or
3cos(x)+1=0
cos(x)=-1/3
x=1.91,4.37(In quadrants II and III where cos<0)