15(x+y)=300 20(x-y)=300 求二元一次方程解全过程!

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 已知x+y+y=20,x+y=15求x.y 化简 x / y(x+y) - y / x(x+y) = x(x+y)(x-y)-y(y+x)(y-x)=(x-y)( )填空 12x+20y=20x+15y x+x+x+y=20 x+x+y=14 x=?y=? x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x+x+y+y+y=21 ,x+x+y+y+y+y+y=27 ,x ,y=? x=15y x+y=20,x-y=10,y= y=x(x 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15 x^2+y^2=15,x+y=7,x＞y,求x-y x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 x+x+x+x+y+y+y=56 x+x+x=15,x+y+y=19,求y-x等于几