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

b-2a等于a?

3-2xy+3yx²+6xy-4x²y =3+4xy-x²y =3+1x2+(-1)²x2 =3+2+2 =7

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

解:4x-5y-3xy-8x+y-2xy =-4x-4y-5xy =-4(x+y)-5xy 代入计算得-4×(-4)-5×(-4)=-16 +20 =4

[(-1/2x^3y^4)^3+(-1/6xy^2)^2*3xy^2]÷(-1/2xy^2)^3 =[(-1/8)x^9 y^12 + (1/36)x²y^4 * 3xy²] ÷[(-1/8)x³y^6] =[(-1/8)x^9 y^12 + (1/12)x³y^6] ÷[(-1/8)x³y^6] =[(-1/8)x^9 y^12]÷[(-1/8)x³y^6] + [(1/12)x...

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=2x2-4xy+4xy-8y2-3x2+4y2-y=-x2-4y2-y,当x=13,y=2时,原式=-19-16-2=-1819.

化简: 1.去括号:xy+yy+xx-2xy+yy-xx-2yy; 2.合并同类项:(xy-2xy)+(yy+yy-2yy)+(xx-xx)=-xy,即是化简后是:-xy 代入数据求解:-xy=-(-1/3)*3=1

先化简,再求值 4x^2y-(3x^3-2xy^2-x^2y)+(xy^2+3x^3+3) 其中x=2,y=-3 解:4x^2y-(3x^3-2xy^2-x^2y)+(xy^2+3x^3+3) = 4x^2y-3x^3+2xy^2+x^2y+xy^2+3x^3+3 =5x^2y+3xy^2+3 当x=2,y=-3时, 原式=5*2^2*(-3)+3*2*(-3)^2+3 =-3

(1).3a^2+(4a^2-2a-1)-2(3a^2-a+1),其中a=-1/2 =3a^2+4a^2-2a-1-6a^2+2a-2 =a^2-3 =1/4-3 =-11/4 (2).2(x^2y+ay^2-xy^2)-(2yx^2-3xy^2+3x^2),其中x=-3,y=2 =2x^2y+2ay^2-2xy^2-2yx^2+3xy^2-3x^2 =xy^2+2ay^2-3x^2 =-12+8a-27 =-39+8a

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