求值:1-sin^6a-cos^6a/1-sin^4a-cos^4a

最后结果是1。5吧?1=(sin^2a+cos^2a)^2=sin^4+2sin^2a×cos^2a+cos^4a 可以明白?1-sin^6a-cos^6a sin^4a+2sin^2a×cos^2a+cos^4a-(sin^6a+cos^6a)--------------- = --------------------------------------------1-sin^4a-cos^4a sin^4a+2sin^2a×cos^2a+cos^4a-(sin^4a+cos^4a) sin^4+2sin^2a×cos^2a+cos^4a-(sin^6a+cos^6a)= --------------------------------------------① 2sin^2a×cos^2a根据立方和公式:sin^6a+cos^6a=(sin^2a)^3+(cos^2a)^3 =(sin^2a+cos^2a)(sin^4a-sin^2a×cos^2a+cos^4a) =sin^4a-sin^2a×cos^2a+cos^4a②把①中sin^6a+cos^6a换成②中的结果可以得: sin^4+2sin^2a×cos^2a+cos^4a-(sin^4a-sin^2a×cos^2a+cos^4a)原式=------------------------------------------------------------- 2sin^2a×cos^2a 3sin^2a×cos^2a = -----------------=1。5 2sin^2a×cos^2a不知道结果对不对。但是思路是正确的。输入的时候排版很好。可是一发布上去就乱了。。你可以看懂不?如果看不懂的话。你给我发消息。。就点儿乱。如果认真看一下还是可以看懂的。--------是分数线。。。真是抱歉~