（1）{x+y=3,3x-y=-1

已知：3x=8y.求（1）x+y/y (2)2x+3y/x-2y 先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y {3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 ｛4/(x+y)+6/(x-y)=3 ｛9/(x-y)-1/(x+y)=1 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 y'=(x-y+1)/(x+y-3)通解 2(x+y) 3x+3y=24 x+y/2x x y/2y= 1 x>1,y>0,且满足xy=x^y,x/y=x^3y,求x+y 10/x+y+3/x-y=-5 15/x+y-2/x-y=-1（用换元法解此方程组） 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 已知x=3分之1,y=二分之一,求代数式x-(x+y）+（x+2y)-(x+3y)+...-(x+13y)的值