Question

Упростите выражение 1-1/sin^2a

Answer 1

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