x^2+y^2=15,x+y=7,x＞y,求x-y

x^2+y^2=15,x+y=7,x＞y,求x-y x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x+2y=2x+y+1=7x-y 求：2x-y? 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15 {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 当x+y=2时7(x+y)一(x+y)+(x+y)=? 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 填空：x-y/x+y=( )/x^2-y^2 （x-y)2•(y-x)³(x-y)=? (x-y)(x-2y)+(x-2y)(x-7y),其中X=4,Y=1.5 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)=?