28/x+18/y=1 化简

化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 y/3-x+1/6=3 2(x-y/2)=3(x+y/18) 1 ,化简 （x-y)(x+y) 2(x+y)-3分之2(x-y)-3（x+y）+3分之2(x-y)化简 其中x=-2,y=1 化简(x+y)+(2x+1/2y)+(3x+2/3y)+(4x+3/4y)+...+(9x+8/9y)=? 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 y=[x-1], 1.已知1/x+1/y=-1/x+y,则y/x+x/y=? {3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1 ｛4/(x+y)+6/(x-y)=3 ｛9/(x-y)-1/(x+y)=1 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1