∵cosa+cos^2a=1 ∵sin^2a+cos^2a=1 ∴sin^2a=cosa∴ sin^2a+sin^6a+sin^8a =sin^2a+(sin^2a)^3+(sin^2a)^4=cosa+cos^3a+cos^4a =cosa+cos^2a(cosa+cos^2a) =cosa+cos^2a(sin^2a+cos^2a)=cosa+cos^2a=sin^2a+cos^2a ...