Question

Преобразование выражений (во вложении) 

Answer 1

$frac {1+cos2a+cos^2a}{sin^2a}=frac{1+2cos^2a-1+cos^2a}{sin^2a}=frac{3cos^2a}{sin^2a}=3c</var><var>tg^2a$
$frac{cos^2a-ctg^2a}{tg^2a-sin^2a}=frac{cos^2a-frac{cos^2a}{sin^2a}}{frac{sin^2a}{cos^2a}-sin^2a}=frac{frac{sin^2acos^2a-cos^2a}{sin^2a}}{frac{sin^2a-sin^2acos^2a}{cos^2a}}=frac{cos^2a(sin^2a-1)}{sin^2a}*\*frac{cos^2a}{sin^2a(1-cos^2a)}=frac{-cos^2a*cos^2a}{sin^2a}*frac{cos^2a}{sin^2a*sin^2a}=frac{cos^6a}{sin^6a}=ctg^6a$