Can somebody help me verify this? -2cos^2xtan(-x)=sin2x
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Originally Posted by unmcintosh Can somebody help me verify this? -2cos^2xtan(-x)=sin2x knowing $\displaystyle \tan(-x)=-tan(x)=\frac{sin(x)}{\cos(x)}$ we multiply by cos²(x) to get $\displaystyle -\sin(x)\cos(x)$ and then dont forget that negative two $\displaystyle 2\sin(x)\cos(x)=\sin(2x)$ QED
when you multiply by cos^2x, how do you get -sinxcosx?
Originally Posted by unmcintosh when you multiply by cos^2x, how do you get -sinxcosx? $\displaystyle \cos^2(x)\cdot\tan(-x)=\cos^2(x)\cdot\frac{-\sin(x)}{\cos(x)}=-\sin(x)\cos(x)$
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