Question

упростите выражение

Answer 1

$frac{Cos^{4}-Sin^{4}alpha}{(1-Sinalpha)(1+Sinalpha)}+2tg^{2}alpha-frac{1}{Cos^{2}alpha}=frac{(Cos^{2}alpha+Sin^{2}alpha)(Cos^{2}alpha-Sin^{2}alpha)}{1-Sin^{2} alpha }+2tg^{2}alpha-(tg^{2}alpha+1)=frac{Cos^{2}alpha-Sin^{2}alpha}{Cos^{2}alpha}+2tg^{2}alpha-tg^{2}alpha-1=1-tg^{2}alpha+tg^{2} alpha-1=0$