Question

Cu cat e egal Cos4x ,??

Answer 1

1-2sin^2x
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Answer 2

$cos4x= cos^{2}x - sin^{2}x$ 
$cos4x= cos^{2}x - sin^{2}x$
$cos4x=1-2sin^{2}x$
$cos4x=2cos^{2}x -1$
$cos4x=sin[tex]( \frac{ \pi }{2} -x)$