Question

Здравствуйте! Помогите,плиз, решить это

Answer 1

$1)Sin\alpha*Ctg \alpha=Sin \alpha* \frac{Cos\alpha} {Sin\alpha}=Cos \alpha\\\\2)tg\alpha*Cos \alpha= \frac{Sin\alpha} {Cos\alpha}*Cos \alpha=Sin \alpha\\\\3)\frac{Sin\alpha} {tg\alpha} =Sin\alpha :\frac{Sin\alpha} {Cos\alpha}=Sin \alpha * \frac{Cos\alpha} {Sin\alpha}=Cos \alpha$

$4)tg\alpha *Ctg\alpha-1=1-1=0\\\\5)\frac{tg\alpha} {Ctg\alpha}+1= \frac{tg\alpha} {\frac{1}{tg\alpha} }+1=tg ^{2} \alpha+1= \frac{1}{Cos^{2}\alpha}\\\\6)\frac{Sin^{2}\alpha-1}{1-Cos^{2}\alpha}= \frac{-Cos^{2}\alpha}{Sin^{2}\alpha}=-Ctg ^{2} \alpha$