证 (sin^2x+sinx cosx -cotx)/(sin^2x-sinx cosx+cotx)=(1-cot^3 x)/(cot^3 x +1)

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证 (sin^2x+sinx cosx -cotx)/(sin^2x-sinx cosx+cotx)=(1-cot^3 x)/(cot^3 x +1)

证 (sin^2x+sinx cosx -cotx)/(sin^2x-sinx cosx+cotx)=(1-cot^3 x)/(cot^3 x +1)
证 (sin^2x+sinx cosx -cotx)/(sin^2x-sinx cosx+cotx)=(1-cot^3 x)/(cot^3 x +1)

证 (sin^2x+sinx cosx -cotx)/(sin^2x-sinx cosx+cotx)=(1-cot^3 x)/(cot^3 x +1)
等式左边
分子分母同时乘以sinx变为
(sin^3x+sin^2x cosx -cosx)/(sin^3x-sin^2x cosx+cosx)
=[sin^3x+(1-cos^2x )cosx -cosx]/[sin^3x-(1-cos^2x) cosx+cosx]
=[sin^3x-cos^3x ]/[sin^3x+cos^3x]
等式右边分子分母同时乘以sin^3x变为
[sin^3x-cos^3x ]/[sin^3x+cos^3x]=左边.证毕