Question

sin^2 a/1+ctg^2a(cos^2a-1) упростить

Answer 1

$\frac{sin^2a}{1+ctg^2a}\cdot (cos^2a-1)=\frac{sin^2a}{\frac{1}{sin^2a}}\cdot (-sin^2a)=-sin^4a\cdot sin^2a=-sin^6a\\\\\\\star sin^2a+cos^2a=1\; \; \star \\\\\star \; \; 1+ctg^2a=\frac{1}{sin^2a}\; \; \star$