1/(x+y)-1/(x+y)=3/20 2/(x+y)+3/(x-y)=19/20 这是1/(x+y)-1/(x+y)=3/20 2/(x+y)+3/(x-y)=19/20 这是一个方程组

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 {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 (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) 2(x+y)-3(x-y)=1 6(x+y)+(x-y)=51 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 变量x,y满足约束条件,x+y>=3,x-y>=-1,2x-y 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 (x-y)^2+(x+y)(x-y) 其中 X =3 Y=-1 1/(x+y)-1/(x-y)=-3/20,2/(x+y)+3/(y-x)=-(1/5)急啊! x+y+2(-x-y+1)=3(1-y-x)-4-(y+x-1),x+y=? {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? 请问60%x+20%y=30%(x+y) 怎么得到x:y=1:3 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 先化简 再求值 (2x-y)(y+x)-(x-2y)(2y+x)-(-3y+x)^2其(√x+1)+y^2+4=-4y