What values are $\displaystyle \theta$? $\displaystyle 18\cos\theta + 9\sin^{2}\theta = 0$ $\displaystyle 9(2\cos\theta + \sin^{2}\theta) = 0$ next move?
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use $\displaystyle sin^2\theta+cos^2\theta=1$
Originally Posted by muddywaters use $\displaystyle sin^2\theta+cos^2\theta=1$ I don't have $\displaystyle cos^{2}\theta$ only $\displaystyle 2\cos\theta$
Originally Posted by Jason76 I don't have $\displaystyle cos^{2}\theta$ only $\displaystyle 2\cos\theta$ try $\displaystyle sin^2\theta=1-cos^2\theta$
and then try to spot the form of a quadratic equation...
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