Question

Досказать что:
ctga/ctga+tga = cos^2a

Answer 1

$\frac{\cot a}{\cot a+\tan a}=\frac{\frac{\cos a}{\sin a}}{\frac{\cos a}{\sin a}+\frac{\sin a}{\cos a}}=\frac{\frac{\cos a}{\sin a}}{\frac{\cos^2 a+\sin^2 a}{\sin a\cos a}}=\frac{\cos a}{\sin a}*\frac{\sin a\cos a}{1}=\cos^2 a$