Question

1+ctg^2a=ctg^2a/cos^2a

Answer 1

1+ctg^2a=ctg^2a/cos^2a

Доказать?

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