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先化简再求值:设:A=2x^2-3xy+y^2-x+2y B=4x^2-6x...

(1)原式=3a-8a+2-3+4a=-a-1,代入a=-12可得:原式=-a-1=-12.(2)原式=2x2y-4xy2+3xy2-x2y=x2y-4xy2,将x=-1,y=2代入得:原式=x2y-4xy2=18.

解:(1)﹣3(2x 2 ﹣xy)+4(x 2 +xy﹣ )=﹣6x 2 +3xy+4x 2 +4xy﹣1)=﹣2x 2 +7xy﹣1,把x=﹣1,y=﹣ 代入﹣2x 2 +7xy﹣1=﹣2+1﹣1=﹣2.(2)∵|x﹣2|+(y+1) 2 =0,则x﹣2=0,x=2;y+1=0,y=﹣1.则﹣2(2x﹣3y 2 )+5(x﹣y 2 )﹣1=﹣4...

解:原式=5x^2y-【4x^2-3-(2x-2x^2y)】+4(xy^2-xyz) =5x^2y-(4x^2-3-2x+2x^2y)+4xy^2-4xyz =5x^2y-4x^2+3+2x-2x^2y+4xy^2-4xyz =(5-2)x^2y+4xy^2-4xyz-4x^2+2x+3 =3x^2y+4xy^2-4xyz-4x^2+2x+3

原式=3x2-3xy+6y2-2x2+4xy-4y2=x2+xy+2y2.当x=-2,y=12时,原式=(-2)2+(-2)×12+2×(12)2=72.

(6x√y/x +3/y√xy³)-(4y√x/y+√36xy), =(6√xy+3√xy)-(4√xy+6√xy) =9√xy-10√xy =-√xy 当x=3/2 y=27时 原式=-√3/2×27=-9√2/2

原式=12x2-18xy+24y2-12x2+21xy-24y2=(12x2-12x2)+(-18xy+21xy)+(24y2-24y2)=3xy,当x=73,y=-5时,原式=3×73×(-5)=-35.

2(x^2 y+xy)-3(x^2 y-xy)-4x^2 y, =2x²y+2xy-3x²y+3xy-4x²y =-5x²y+5xy =-5x(-1)²x1+5x(-1)x1² =-5-5 =-10

原式=[9x5y2-54x5y6]÷9x4y2=x-6xy4,当x=13,y=2时,原式=13-6×13×2=-323.

(1)两边同乘以0.1得:0.5(x-1)-0.2(x+1)=0.2,去括号得:0.5x-0.5-0.2x-0.2=0.2,移项得:0.5x-0.2x=0.2+0.5+0.2,合并同类项:0.3x=0.9,系数化为l,得x=3;(2)原式=5x 2 y-2xy 2 -3xy-2xy-5x 2 y=-xy(4y+5),把x=- 1 3 ,y=- 1 4 ...

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