Question

Упростите выражение (1+ctg^2a)*(1-sin^2a)

Answer 1

$(1+ctg^2 alpha )(1-sin^2 alpha )= dfrac{1}{sin^2 alpha } cdot (1-sin^2 alpha )=dfrac{1}{sin^2 alpha }cdot cos^2 alpha =ctg^2 alpha$