Question

Упростите выражения:

a)1+ctg2a-1

                   sin²

b)1-cos²a

      sin²a        -cos²a

Answer 1

a)$1+ctg^2a-frac{1}{sin^2a}=frac{1}{sin^2a}-frac{1}{sin^2a}=0$

б) $frac{1-cos^2a}{sin^2a}-cos^2a=frac{sin^2a}{sin^2a}-cos^2a=1-cos^2a=sin^2a$