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①计算:(﹣x 2 +2xy﹣y 2 )﹣2(xy﹣3x 2 )+3(...

解:①原式=﹣x 2 +2xy﹣y 2 ﹣2xy+6x 2 +6y 2 ﹣3xy=5x 2 +5y 2 ﹣3xy;②原式=5a 2 b﹣{2a 2 b﹣[3ab 2 ﹣4ab 2 +2a 2 b]}=5a 2 b﹣{2a 2 b﹣3ab 2 +4ab 2 ﹣2a 2 b}=5a 2 b﹣2a 2 b+3ab 2 ﹣4ab 2 +2a 2 b=5a 2 b﹣a 2 b;当a=﹣3,b=0.5时,...

解:原式=6xy﹣9x 2 y﹣6xy+3x 2 y=﹣6x 2 y.

解:原式=3x 2 y﹣(2x 2 y﹣6xy+3x 2 y﹣xy)=3x 2 y﹣2x 2 y+6xy﹣3x 2 y+xy=﹣2x 2 y+7xy.

解:(1)原式=2a 2 ﹣2ab﹣2a 2 +3ab=ab; (2)原式=﹣x 2 +2xy﹣y 2 ﹣2xy+6x 2 +6y 2 ﹣3xy=5x 2 ﹣3xy+5y 2 .

解:①原式=3x 2 ﹣6xy﹣[3x 2 ﹣2y﹣6xy﹣2y],=3x 2 ﹣6xy﹣3x 2 +2y+6xy+2y,=4y;②﹣B+2A=﹣(2ab﹣3b 2 +4a 2 )+2(3a 2 +b 2 ﹣5ab),=2a 2 ﹣12ab+5b 2 ,当a=﹣ ,b=2时,原式=2 ﹣12(﹣ )×2+5×2 2 =32.5;③原式=(2x 2 +ax﹣y+6)...

解:①3a+2b﹣5a﹣b=﹣2a+b; ②2(x 2 y+xy 2 )﹣2(x 2 y﹣x)﹣2xy 2 ﹣2y,=2x 2 y+2xy 2 ﹣2x 2 y+2x﹣2xy 2 ﹣2y,=2x﹣2y,x=﹣2,y=2时,原式=2×(﹣2)﹣2×2=﹣8.

(1)原式=2a2-2ab-2a2+3ab=ab;(2)原式=-x2+2xy-y2-2xy+6x2+6y2-3xy=5x2-3xy+5y2.

(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.

(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.

(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=-...

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