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3x 2 5xy 2y 2 x 9y 4

3x^2+5xy-2y^2+x+9y-4=3x^2+(5y+1)x-(2y^2-9y+4)=3x^2+(5y+1)x-(y-4)(2y-1)=(3x-y+4)(x+2y-1)十字交叉

答案如下:

(1)3x2+5xy-2y2+x+9y-4=(3x-y)(x+2y)+x+9y-4=(3x-y)(x+2y)-(3x-y)+4x+8y-4=(3x-y)(x+2y-1)+4(x+2y-1)=(3x-y+4)(x+2y-1);(2)a3+1=(a+1)(a2-a+1)(3)4x4-13x2+9=(4x2-9)(x-1)=(2x+3)(2x-3)(x+1)(x-1);...

令t=x+1/x,则x²+1/x²=t²-2,原式:2(t²-2)-3t-1=0 即2t²-3t-5=0,解得t=3或者-1/2 即x+1/x=3或x+1/x=-1/2 而x+1/x=5/2,化简得2x²-5x+2=0 即(x-2)(2x-1)=0,解得x=2或1/2 x+1/x=-1化简得x²+x+1=0无解 综上:x=2...

用双十字相乘法分解因式: 3x²+5xy-2y²+x+9y-4 =(3X-Y+4)(X+2Y-1)。

原式=(x3+3x2y-5xy2+9y3)+(-2y3+2xy2+x2y-2x3)-(4x2y-x3-3xy2+7y3)=x3+3x2y-5xy2+9y3-2y3+2xy2+x2y-2x3-4x2y+x3+3xy2-7y3=(1-2+1)x3+(3+1-4)x2y+(-5+2+3)xy2+(9-2-7)y3=0∴无论x,y取何值,原式的值均为常数0.

(x-y)^2+(x-1/2z)^2+(y-1/2z)^2-3xy-3/2z^2

(1)原式=4x+3x2-3x-2x2-x+x2-1=2x2-1,当x=-1时,原式=2-1=1;(2)原式=4x2y-5xy+8xy-4+x2y+3=5x2y+3xy-1,∵|x-12|+|y+4|=0,∴x=12,y=-4,则原式=-5-6-1=-12.

y/x=3/4 , 令y=3k,y=4k k不等于0 代入: (3x^2-5xy+2y^2)/(2x^2+3xy-5y^2) =(3*16k^2-60k^2+18k^2)/(2*16k^2+36k^2-5*9k^2) =(48-60+18)/(32+36-45) =6/23

(1)原式=-94ab+5;(2)原式=2xy-xy3+6x+1;(3)原式=4x2y-5xy2-3x2y+4xy2=x2y-xy2;(4)原式=5a2+2a-1-12+32a-8a2=-3a2+34a-13.

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