x+y=2009(1),3x+5y-1+a=0(2),5x+3y+2a=0(3)解方程

(x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? 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=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-(x+2009y)的值. 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-(x+2009y)的值. 5(x-y)³-3（x-y）²+7(x-y)-5(x-y)³+（x-y）²-5（x-y）,其中,x-y=1/3.5(x-y)³-3（x-y）²+7(x-y)-5(x-y)³+（x-y）²-5（x-y）,其中,x-y=1/3先化简,再求值； （2x+y-1)(2x-y+1)-(3x+y)(3x-y),其中x=5分之1, x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x (x+2y)(x-2y)-(2x-y)的平方+(3x-y)(2x-5y)其中x=-1 y=13分之1 y(x+y)+(x-y)²-（x+y）（x-y）,其中x=-1/3,y=3 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 y''-5y'+6y=3x+1通解 {x+y=1 ,xy=-6{x(2x-3)=0,y=x²-1{(3x+4y-3)(3x+4y+3)=0,3x+2y=5{(x-y+2)(x+y)=0,x²+y²=8{(x+y)((x+y-1)=0,(x-y)(x-y-1)=0 {3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1 y'=(x-y+1)/(x+y-3)通解 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 (x+y)/6+(x-y)/10=1,(x+y)/6-(x-y)/10=5