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Решите задачу:

$1)\frac{Sin^{2}\alpha}{Cos\alpha-1 }=\frac{1-Cos^{2}\alpha}{Cos\alpha-1 }=\frac{(1-Cos\alpha )(1+Cos\alpha) }{Cos\alpha-1 }=-(1+Cos\alpha)\\\\2)1-Cos^{2}\alpha+tg^{2}\alpha*Cos^{2}\alpha=Sin^{2}\alpha+\frac{Sin^{2}\alpha}{Cos^{2}\alpha}*Cos^{2} \alpha = Sin^{2}\alpha+Sin^{2} \alpha=2Sin^{2}\alpha$ $3)\frac{1-Sin^{2}\alpha}{1-Cos^{2}\alpha}+tg\alpha*Ctg\alpha=\frac{Cos^{2}\alpha }{Sin^{2}\alpha}+1=Ctg^{2}\alpha+1=\frac{1}{Sin^{2}\alpha}$