Question

8sin^2a*cos^2a-1(упростить)

Answer 1

$8sin^2alphacdot cos^2alpha -1=2cdotBig(2cdotsinalpha cosalphaBig)^2-1=\\=2cdotBig(sin(2alpha )Big)^2-1=-Big(1-2sin^2(2alpha)Big)=\\boldsymbol{=-cos(4alpha) }$

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Использованы формулы

$2sinbeta cdot cosbeta =sin(2beta )\\1-2sin^2beta =cos(2beta )$