Question

докажите тождество 1/1+tg^2x + sin^4x+sin^2xcos^2x=1

Answer 1

$frac{1}{1+ tg^{2}x } + sin^{4} x+ sin^{2} x* cos^{2} x=1$
$1+ tg^{2} x= frac{1}{ cos^{2} x}$
$frac{1}{1+ tg^{2} x} =1: frac{1}{ cos^{2}x } = cos^{2}x$
$cos^{2} x+sin^{4}x+ sin^{2} x* cos^{2} x=1$
$cos^{2}x+ sin^{2}x*( sin^{2}x+ cos^{2}x )=1$
$cos^{2}x+ sin^{2}x=1$

1=1