2x^2-7x+7=0 2y^2-7y+8=0x和y旳值?

7y(x-3y)-2(3y-x)=0 .x=?,y=? x+2y=2x+y+1=7x-y 求：2x-y? 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 x^2+y^2=15,x+y=7,x＞y,求x-y {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 当x+y=2时7(x+y)一(x+y)+(x+y)=? 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 化简3(x-y)-7(x--y)+2(y-x) (x-y)(x-2y)+(x-2y)(x-7y),其中X=4,Y=1.5 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 求f(x,y)=x+y+7的最大值,使(x,y)满足x+2y≤10,2x+y≥6,y≥0 {2x+y/3-2y=0 2(2x+y)-5=7y {x+2y+2=0 {7y-4y=-41 求X和Y x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x+2y+2=0 7x-4y=-41 求x和y y^2+2y-x=3x^7,x=0时y的导数 已知(x-y)^2+|5x-7y-2|=0,求x,y的值. 已知|5x-y-8|+(7y-x+2)=0则4x+6y