Question

sin a/1+cos a + sin a/ 1-cos a = 2/sin a тождество

Answer 1

$\frac{\sin\alpha}{1+\cos\alpha}+\frac{\sin\alpha}{1-\cos\alpha}=\frac{\sin\alpha-\sin\alpha\cos\alpha+\sin\alpha+\sin\alpha\cos\alpha}{(1+\cos\alpha)(1-\cos\alpha)}=\frac{2\sin\alpha}{1-\cos^2\alpha}=\frac{2\sin\alpha}{\sin^2\alpha}=\frac2{\sin\alpha}$