已知y=2x-1,若2y-7x=13,则x=

已知y=2x-1,若2y-7x=13,则x= 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 若x-y=2(x+y),求代数式x-y/x+y+x+y/x-y求代数式 x+y分之x-y+x-y分之x+y 已知:y=ax的3次方+bx+3,当x=-1/2时,y=-7,试求x=1/2时,y的值 已知f(x+y,y/x)=x^2-y^2,则f(x,y)= 已知（x+y)^2=9,x^2+y^2=7,则xy=?已知（x+y)^2=9,x^2+y^2=7,则xy=?已知（x+y)^2=4,（x-y）^2=3,则x^2+y^2=?若x^2+y^2=3,xy=1,则x-y=? 已知1/x-1/y=3,则代数式x(2-7y)-y(7x+2)/x(1-y)-y(x+1)的值为多少. 已知方程组{(X+Y)-3(X-Y)=7,2(X+Y)+(X-Y）=-7}则(X+Y)(X-Y)= 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 已知(x-y)/13=y/7,则（x+y）/y=已知x/6=y/4=z/3(x,y,z均不为零）,则(x+3y)/(3y-2z)= 已知x属于R,y>0,集合A={x|x*x+x+1,-x,-x-1},集合B={-y,-y/2,y+1}若A=B,则x*x+y*y的值为 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 已知x+2y=3则x=? x-y=7则y=? 已知|x-2y|+|5x-7y-2|则,x = y= 已知(x+y)^2-2x+2y+1=0,则(x+y)^999= 已知|5x-y-8|+(7y-x+2)=0则4x+6y 已知（x+y)²-2（x+y）+1=0,则x+y=? 已知y=x-1,则代数式(x-y)2+y-x+1的值为 已知X和Y满足3X+4Y=2,X-Y-1/7