Question

Помогите решить 2 и 4
9 класс ​

Answer 1

2)Cos²2α + 4Sin²αCos²α = Cos²2α + Sin²2α = 1

$4)\frac{Cos^{2}2\alpha}{Ctg\alpha-tg\alpha}=\frac{Cosx^{2}2\alpha}{\frac{Cos\alpha }{Sin\alpha }-\frac{Sin\alpha }{Cos\alpha}}=\frac{Cos^{2}2\alpha}{\frac{Cos^{2}\alpha-Sin^{2}\alpha}{Sin\alpha Cos\alpha}}=\frac{Cos^{2}2\alpha}{\frac{Cos^{2}2\alpha}{Sin\alpha Cos\alpha}}=\frac{Cos^{2}2\alpha*Sin\alpha Cos\alpha }{Cos^{2}2\alpha} =Sin\alpha Cos\alpha =\frac{Sin2\alpha}{2}$