Question

Помогите умоляюююю не хочу 2
решать цыфру 2).​

Answer 1

$\sin^2\alpha(1 + \mathrm{ctg}^2\alpha)-\cos^2\alpha=\sin^2\alpha\\\\\sin^2\alpha(1 + \mathrm{ctg}^2\alpha)=\sin^2\alpha + \cos^2\alpha\\\\\sin^2\alpha(1 + \mathrm{ctg}^2\alpha)=1\\\\\sin^2\alpha\left(1 + \dfrac{\cos^2\alpha}{\sin^2\alpha}\right)=1\\\\\sin^2\alpha + \sin^2\alpha\dfrac{\cos^2\alpha}{\sin^2\alpha}\right=1\\\\\sin^2\alpha + \cos^2\alpha=1\\\\1=1$