Question

помогите 85(1).........

Answer 1

$sin^4a-sin^2a+cos^2a=sin^2acdot (sin^2a-1)+cos^2a=\\=(1-cos^2a)cdot Big (-(1-sin^2a)Big )+cos^2a=\\=-(1-cos^2a)cdot cos^2a+cos^2a=-cos^2a+cos^4a+cos^2a=cos^4a$