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tekilochka [14]
3 years ago
15

Prove that cos^3x+3cos2x= 4 (cos^6 x-sin^6x)

Mathematics
1 answer:
gavmur [86]3 years ago
5 0
But this isn't true... If x=\dfrac\pi2, you have

\cos^3\dfrac\pi2+3\cos\pi=0-3=-3
4\left(\cos^6\dfrac\pi2-\sin^6\dfrac\pi2\right)=4(0-1)=-4

but of course -3\neq-4.
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