Question

6.14 помогите решить

Answer 1

$displaystyle frac{sin^4a-sin^2a+cos^2a}{cos^3a}=frac{sin^2a(sin^2a-1)+cos^2a}{cos^3a}=\\=frac{sin^2acdot(-cos^2a)+cos^2a}{cos^3a}=frac{cos^2a(1-sin^2a)}{cos^3a}=frac{cos a}{cos a}=boxed{1}\\\sin^2a+cos^2a=1$