sin^6a+cos^6a-2sin^4a-cos^4a+sin^2a=0我想知道,这道题为什么等于零,

左边=(sin^2a+cos^2a)(sin^4a-sin^2acos^2a+cos^4a)-2sin^4a-cos^4a+sin^2a
=sin^4a-sin^2acos^2a+cos^4a-2sin^4a-cos^4a+sin^2a
=-sin^4a-sin^2acos^2a+sin^2a
=sin^2a(1-sin^2a)-sin^2acos^2a
=sin^2acos^2a-sin^2acos^2a
=0=右边

原式左边=cos^4A*(cos^2A-1)+(sin^3A-sinA)^2
=-sin^2Acos^4A+sin^2A(sin^2A-1)^2
=-sin^2Acos^4A+sin^2A(-cos^2A)^2
=-sin^2Acos^4A+sin^2Acos^4A
=0