题有点问题吧 应该是求sin^2A+sin^6A+sin^8A等于多少因为cosa+cos^2a=1又因为sin^2a+cos^2a=1所以得:sin^2a=cosa则: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...