Question

$cos^{2} alpha(1+tg^2 alpha )$=
помогите

Answer 1

Формула
$1+tg^2 alpha =frac{1}{cos^2 alpha }\\cos^2 alpha (1+tg^2 alpha )=cos^2 alpha cdot frac{1}{cos^2 alpha }=1\\sin^2 alpha (1+tg^2 alpha )=sin^2 alpha cdot frac{1}{cos^2 alpha }=(frac{sin alpha }{cos alpha })^2=tg^2 alpha$