先化简,后求值:x² 2x-8 x³ 2x² x

原式=[(x+2)/(x^2-2x)-(x-1)/(x^2-4x+4)]÷2(x-4)/(x^3-2x^2)=[(x+2)/(x^2-2x)-(x-1)/(x-2)²)]*[x²(

3x(2x²-4x+3)-2x²(3x+4)=6x^3-12x^2+9x-6x^3-8x^2=x(9-20x)将x=-2带进去结果=-98

原式=5x2y+{xy-[5x2y-7xy2-12xy]-4x2y-xy}-7xy2=5x2y+{xy-5x2y+7xy2+12xy-4x2y-xy}-7xy2=5x2y+xy-5x2y+7xy2+1

原式=(x−2)(x+4)x(x+1)2÷(x−2)(x+4)x(x+1)=(x−2)(x+4)x(x+1)2×x(x+1)(x−2)(x+4)=1x+1，当x=-45时，原式=1−45+1=5．

由[x/（x-2)-x/（x+2)]÷4/（2-x）=[（x²+2x-x²+2x）/（x-2）（x+2)]/4/（2-x）=4x/（x-2）（x+2)×（2-x）/4=-x/（x+

x(x^2-6x-9)-x(x^2-8x-15)+2x(3-x)=x^3-6x^2-9x-x^3+8x^2+15x+6x-2x^2=12x=36

(3x/x+1-x/x-1)+x-2/x的平方-1=(3x(x-1)-x(x+1))/(x+1)(x-1)+x-2/x^2-1=(3x^2-3x-x^2-x+x-2)/(x^2-1)=(2x^2-3x

X(X^2-6X-9)-X(X^2-8X-15)+2X(3-X)=X^3-6X^2-9X-X^3+8X^2+15X+6X-2X^2=12x带入X=1/3原式=12*1/3=4

x+y也有平方的原式=(x²-2xy+y²-x²-2xy-y²)/2xy=-4xy/2xy=-2再问：我是怎么写的最后【-4xy】/（2x）可是再后=-2y再答

(x-y)^2+7(x+y)-11(x-y)^2-8(x+y),=-10(x-y)²-(x+y)当x+y=-3,x-y=-1时=-10*(-1)²-(-3)=-10+3=-7

[（x-1)/x-(x-2)/(x+1)]÷[(2x^2-x)/(x^2+2x+1)]=[(x-1)(x+1)-x(x-2)]/x(x+1)÷[x(2x-1)/(x+1)^2=(2x-1)/x(x+1

2x的平方-5x+x的平方+4x-3x的平方-2=-x-2=-1/2-2=-5/2

x^3+2x^2+x/x^2+2x-8除以（x/x-2×x+1/x+4)=x(x^2+2x+1)/(x-2)(x+4)/(x(x+1)/(x-2)(x+4))=x(x+1)^2/(x-2)(x+4)*

(3x+1)(2x-3)-(6x-5)(x-3)=(6x²-7x-3)-(6x²-23x+15)=6x²-7x-3-6x²+23x-15=16x-18把x=3代

原式=(x+2)(x+3)x+3•x−3(x+2)(x−2)−1=x−3x−2−x−2x−2=−1x−2；当x=3时，原式=−13−2=2+3．

能不能先用（）把每个分数括起来?

再答：我这么诚心，还写出来了，给个采纳吧！

[1/(x+1)+(x^2-2x+1)/(x^2-1)]÷（x-1)/(x+1)=[1/(x+1)+(x-1)^2/(x+1)(x-1)]*(x+1)/(x-1)=[1/(x+1)+(x-1)/(x+

原式=〖（x+2）/x(x-2)-(x-1)/(x-2)^2〗÷〖(x-4)(x+4)/x(x+4)〗=〖(x+2)(x-2)-(x-1)x〗/x(x-2)^2〗÷〖(x-4)(x+4)/x(x+4)

原式=x+8(x−2)2•x(x−2)x+3+1x−2•x(x−2)x+3=x(x+8)(x−2)(x+3)+x(x−2)(x−2)(x+3)=2x(x+3)(x−2)(x+3)=2xx−2，方程x2