Question

1) 1-1/sin^2L
2)4-tgL*ctgL
3)cos^2b-cos^2bsin^2b

Answer 1

$1-frac{1}{sin^2a}=frac{sin^2a}{sin^2a}-frac{1}{sin^2a}=frac{sin^2a-1}{sin62a}=frac{-(1-sin^2a)}{sin^2a}=frac{-cos^2a}{sin^2a}=-ctg^2a\\4-tga*ctga=4-frac{sina}{cosa}*frac{cosa}{sina}= 4-1=3\\cos^2beta-cos^2beta*sin^2beta=cos^2beta(1-sin^2beta)=cos^2beta*cos^2beta=cos^4beta$