SOLUTION: ind all the solutions of the equation in the interval 0 2pi cos 2 theta= 1-3 cos theta

Question 814141: ind all the solutions of the equation in the interval 0 2pi cos 2 theta= 1-3 cos theta
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
Find all the solutions of the equation in the interval [0,2pi] cos 2 theta= 1-3 cos theta
***
cos(2x)=1-3cos(x)
2cos^2(x)-1=1-3cos(x)
2cos^2(x)+3cos(x)-2=0
(2cosx-1)(cosx+2)=0
..
2cosx-1=0
cosx=1/2
x=π/3,5π/3
or
cosx+2=0
cosx=2 (reject, -1 < cosx < 1)

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