By using the expansion of $\cos\left(A+B\right)$cos(A+B), verify $\cos2x=2\cos^2\left(x\right)-1$cos2x=2cos2(x)−1.

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By using the expansion of $\sin\left(A+B\right)$sin(A+B), verify that $\sin2x=2\sin x\cos x$sin2x=2sinxcosx.

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