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

解:原式=3x 2 y﹣[2xy 2 ﹣2xy+2x 2 y]+2xy 2 =3x 2 y﹣2xy 2 +2xy﹣2x 2 y+2xy 2 =x 2 y+2xy,当x=3,y=﹣1时,原式=3 2 ×(﹣1)+2 ×3 ×(﹣1)=﹣9﹣6=﹣15.

①原式=-8a7b4+4a4b5-12a3b2;②原式=12x3y3-3x4y2-8x2y4+2x3y3=14x3y3-3x4y2-8x2y4.

(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=-...

3x2-2xy+12y2=47① 2x2+xy+8y2=36② ①*36-②*47,得14x^2-119xy+56y^2=0, 2x^2-17xy+8y^2=0, (x-8y)(2x-y)=0, ∴x=8y,③或y=2x④ 由①③解得(x,y)=(4,1/2),(-4,-1/2); 由①④解得(x,y)=(1,2),(-1,-2). ∴x^2+4y^2=17, x^2-4y^2=土15, 于是x^4-16y^4=土255.

x²y+xy²=xy(x+y)=1*3=3 x²+y²=(x+y)²-2xy=3²-2=7

①原式=3x2-6xy-3x2+2y+6xy+2y=4y;②-B+2A=-(2ab-3b2+4a2)+2(3a2+b2-5ab)=-2ab+3b2-4a2+6a2+2b2-10ab=2a2+5b2-12ab;当a=-12,b=2时,-B+2A=2×(?12)2+5×22-12×(-12)×2=12+20+12=3212.

解:∵|x|=3,∴x=±3;∵y 2 =16,∴y=±4;∵|x+y|=1,∴x+y=±1;∴x=3,y=﹣4或x=﹣3,y=4.∴xy=﹣12;∴A=4x 2 ﹣2xy+4y 2 =4(x+y) 2 ﹣10xy=4+120=124;B=3x 2 ﹣6xy+3y 2 =3(x+y) 2 ﹣12xy=3+144=147;∴4A+[(2A﹣B)﹣3(A+B)]=3A﹣4B=3×124...

(2x3-3x2y-2xy2)-(x3-2xy2+y3)+(-x3+3x2y-y3)=2x3-3x2y-2xy2-x3+2xy2-y3-x3+3x2y-y3=(2-1-1)x3+(-3+3)x2y+(-2+2)xy2+(-1-1)y3=-2y3,故代数式的值与x的取值无关.

(x+1)的2次方+丨y-1/2丨=0 ∴x+1=0 y-1/2=0 ∴x=-1 y=1/2 2(xy的2次方+x的2次方y)-[2xy的2次方-3(1-x的2次方y)]-2 =2xy²+2x²y-2xy²+3-3x²y-2 =-x²y+1 当x=-1,y=1/2时 原式=-1/2+1=1/2

(x+2)²+|x+y-10|=0 x+2=0 x+y-10=0 x=-2 y=12 3x²y-[5x²y-﹙2xy-x²y﹚-2x²]-xy =3x²y-(5x²y-2xy+x²y-2x²)-xy =3x²y-(6x²y-2xy-2x²)-xy =3x²y-6x²y+...

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