Question

упростите пожалуйста
${ cos }^{2} alpha : : (1 - tg {}^{2} alpha )$

Answer 1

${ cos }^{2} alpha : : (1 - tg {}^{2} alpha )={ cos }^{2} alpha-{ cos }^{2} alpha*frac{{ sin }^{2} alpha}{{ cos }^{2} alpha} =\={ cos }^{2} alpha-{ sin }^{2} alpha=cos2alpha$