(8xy-3x2)-5xy-3(xy-2x2+3)已知A=x3+x2-x+1,B=-x3-x2+x+1,当x=-2时,求A-2B的值.

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(8xy-3x2)-5xy-3(xy-2x2+3)已知A=x3+x2-x+1,B=-x3-x2+x+1,当x=-2时,求A-2B的值.
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(8xy-3x2)-5xy-3(xy-2x2+3)已知A=x3+x2-x+1,B=-x3-x2+x+1,当x=-2时,求A-2B的值.
(8xy-3x2)-5xy-3(xy-2x2+3)
已知A=x3+x2-x+1,B=-x3-x2+x+1,当x=-2时,求A-2B的值.

(8xy-3x2)-5xy-3(xy-2x2+3)已知A=x3+x2-x+1,B=-x3-x2+x+1,当x=-2时,求A-2B的值.
A=-6-4+2+1=-7,B=6+4-2+1=9
A-2B=-7-2x9=-25

(8xy-3*2)-5xy-3(xy-2*2+3)=8xy-6-5xy-(3xy-12+9)=-6+12-9=-3
A-2B=x3+x2-x+1-2(-x3-x2+x+1)=3x3+3x2-3x-1=3(x3+x2-x)-1
当x=-2时，即3*（-8+4+2）-1=-7

(1)(8xy-3x2)-5xy-3(xy-2x2+3)=8xy-3x2-5xy-3xy+6x2-9=3x2-9=3*4-9=3
(2)A=-8+4+2+1=-1
B=8-4-2+1=3
A-2B=-1-2*3=-7

①原式=8xy-6-5xy-3xy+12-9=-3
②∵A=x3+x2-x+1
∴A=4X+1
∵B=-x3-x2+x+1
∴B=-4X+1
∴A-2B=4X+1-2（-4X+1）=12X-1
当X=-2时，12X-1=12×（-2）-1=-25

(-3xy+2xy)-(4xy+xy) 已知x2-3xy=-5,xy+y2=3,求x2-2xy+y2. (3xy-9x2-2y2-6xy)-(6x2+2xy-3xy-y) 2(x2-xy)-3(2x2-3xy)-2[x2-(2x2-xy+y2)] 化简. 5x2*3xy= 2(x-xy)-3(2x2-3xy）2[x2（2x2-xy+y2)] -（x2-2xy-y2)+(5x2-2xy-3y2)-（x2-2xy-y2)+(5x2-2xy-3y2)化简 4x2-3y2+2xy-4x2+5x2 若3x2-4xy+y2=-3,2x2+3xy-2y2=8,求5x2-18xy+7y2的值. 3xy-3xy-xy+2yx 3xy-4xy-（-2xy） 3xy-4xy-（-2xy） 2xy.(-3xy)÷(xy) 2xy-xy-(-3xy)= 已知x2+xy=3,xy+y2=-2,则2x2-xy-3y2= 2xy(5xy的2次方+3xy-1) 2xy(5xy的2次方+3xy-1) xy×(xy)²-3xy