(x+2)乘以(x+3)减x乘以(x+1)减8 =x2+3x+2x+6-x2-x-8=4x-2
(x+2)*(x+3)-x(x+1)-8=x平方+5x+6-x平方-x-8=4x-2
=x^2+5x+6-x^2-x-8=4x-2
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