Question 965359: sin(2x)sinx - cos(2x)cosx = 1 where x is (-pi, pi)
Answer by lwsshak3(11628)   (Show Source):
You can put this solution on YOUR website! sin(2x)sinx - cos(2x)cosx = 1 where x is (-pi, pi)
2sinxcosxsinx-(cos^2(x)-sin^2(x))cosx=1
2sin^2(x)-cos^2(x)+sin^2(x)=1
3sin^2(x)-cos^2(x)=1
3-3cos^2(x)-cos^2(x)=1
4cos^2(x)=2
cos^2(x)=2/4=1/2
cosx=±√(1/2=±√2/2
x=-3π/4, -π/4, π/4, 3π/4
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