2x+y=15 x+2y=18 x=?y=?

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x^2+y^2=15,x+y=7,x＞y,求x-y 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15 填空：x-y/x+y=( )/x^2-y^2 （x-y)2•(y-x)³(x-y)=? y+y'-2y=2x 微分方程y - 2y' + y = x (x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= (x+y)(x-y)+(x-y)平方-(x-y)(3x-y) 其中x=-2 y=3分之一 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) (x-4y)(2x+y)= (x+y)(2x-3y)=? x+y>=2,x-y x+y>=2,x-y y'-2y=(e^x)-x y'+2y/x=x通解 dy/dx=(2x*x*x*y-y*y*y*y)/(x*x*x*x-2x*y*y*y) {2x+y=15 x+2y=18