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化简:(1)2(2a-3b)+3(2b-3a)(2)2(x2-xy)...

(1)2(2a-3b)+3(2b-3a)=4a-6b+6b-9a=-5a;(2)2(x2-xy)-3(2x2-3xy)-2[x2-(2x2-xy+y2)]=2x2-2xy-6x2+9xy-2x2+4x2-2xy+2y2=(2x2-6x2-2x2+4x2)+(-2xy+9xy-2xy)+2y2=-2x2+5xy+2y2.

(1)原式=2x2-4xy-3y2+9xy=2x2+5xy-3y2;(2)原式=2a-(3b-5a-3a+5b)=2a-3b+5a+3a-5b=10a-8b;(3)原式=-x2+2xy-y2-2xy+6x2+6x2-3xy=-11x2-3xy-y2.

解:(1)原式=3a-2b+5a-7b-4a+8b =3a+5a-4a-2b-7b+8b=4a-b; (2)原式= - = + + -2 ;(3)原式=-x 2 +2xy-y 2 -2xy+6x 2 +6y-3xy=-x 2 +6x 2 +2xy-2xy-3xy-y 2 +6y 2 =5x 2 -3xy+5y 2 。

(1)原式=-2ab+3a-4a+2b+2ab=2b-a;(2)原式=xy- 2 3 y- 2 3 - 1 2 x+ 1 2 xy-1= 3 2 xy- 2 3 y- 1 2 x- 5 3 ,当x= 2 3 ,y= 3 4 时,原式= 3 2 × 2 3 × 3 4 - 2 3 × 3 4 - 1 2 × 2 3 - 5 3 =- 7 4 .

(1)原式=5b-2a-9a+6b=-11a+11b=11(b-a),∵b-a=2,∴原式=11×2=22.(2)原式=6x2-2xy-3x2+5xy=3x2+3xy,当x=-3,y=2时,原式=3×9+3×(-3)×2=27-18=9.

(1)原式=4a2+18a-9a2-12a+3=-5a2+6a+3;(2)原式=3x2-6xy-9x2+6y-6xy-6y=-6x2-12xy,当x=12,y=-34时,原式=-32-6×34=-20512.

解(1)原式=3a+a2-3a-6=a2-6;(2)原式=a3b2-6a3b3;(3)原式=-4xy+9xy2.

解:(1)原式=4y;(2)原式=2a 2 -12ab+5b 2 当a=- ,b=2时,原式=32.5。

(1)①A+B+C=x2-3xy+y2-2xy-x2+2y2=-5xy+3y2;②2A-B-2C=2(x2-3xy)-(y2-2xy)-2(-x2+2y2)=2x2-6xy-y2+2xy+2x2-4y2=4x2-4xy-5y2;(2)2(3x2y-xy2)-(xy2+6x2y)+1=6x2y-2xy2-xy2-6x2y+1=-3xy2+1,∵|x-1|+(y+2)2=0,∴x=1,y=-2,则原式=-...

(1)原式=4x2,将x=-12代入得:原式=1.(2)∵A=2x2+4xy-2x-3,B=-x2+xy+2∴3A=3(2x2+4xy-2x-3)=6x2+12xy-6x-9,∴6B=6(-x2+xy+2)=-6x2+6xy+12,∴3A+6B=(6x2+12xy-6x-9)+(-6x2+6xy+12)=6x2+12xy-6x-9-6x2+6xy+12=18xy-6x+3=6x(3y-1)+3...

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