(3x^2)^3-7x^3[x^3-x(4x^2+1]+(-x^2)^2,其中x=2分之1我算出来是5/4,但是是错的,可我把1/2代进去,算出来是5/4,百度知道上说是87/68,我很纠结,到底是什么?

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