Kirsten M.

asked • 02/25/15

what are the exact solutions of cos 2x + sin x = 0 within [0,2pi)

I think the solutions are 3pi/4 and 7pi/4, but I'm not sure.

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SURENDRA K. answered • 02/25/15

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sin x + cos 2x
sinx+1-2(sin x)^2=0
2(sin x)^2-sinx-1=0
 
sin x =1 or -1/2
 
x=pi/2  or 7pi/6
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Chris M.

Just got this question in Precal, and this is not the correct answer. Surendra, you factored incorrectly. The real answers come out to be sinx=-1 and -1/2, not positive 1 and -1/2. That means your answers are Pi/6, 3Pi/2, and 5Pi/6.
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11/17/15

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