若{X=-1,Y=2,{X=2,Y=1都是关于X,Y的方程AX+BY=5的解,则2A-3B=

若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 若y/x,1/y,1/(x+y)都有意义,则下列等式中,不一定成立的是,说明理由xy/(x^2y)=1/x1/(x-y)=(x+y)/(x^2-y^2)y/(x+1)=y^2/(xy+y)y/(x+y)=(xy-y^2)/(x^2-y^2) 若x*x+y*y=x+y-1/2,求x,y的值如题 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 若y/x,1/y,1/(x+y)都有意义,则下列等式中,不一定成立的是,说明理由xy/(x^2y)=1/x1/(x-y)=(x+y)/(x^2-y^2)y/(x+1)=y^2/xy+yy/(x+y)=(xy-y^2)/(x^2-y^2)第三个是错的 已知x,y都为正整数,且x*x+y*y/2=1,求x*x*(1+y*y)开根号后的最大值. （x-y)(x+y)-(x+y)^2+2y(y-x),其中x=1,y=3. 2y(x+二分之一y)-[(x+y)(x-y)+2y(y+x)],其中|x-1|=2 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 x,y都大于零,若x+y=5,求(x+1/x)(y+1/y)的最小值? x+2y=2x+y+1=7x-y 求：2x-y? 若变量x,y满足约束条件{x>=-1;y>=x;3x+2y 设x,y满足约束条件x+y>=1,x-y>=-1,2x-y 设x,y满足约束条件x+y>=1,x-y>=-1,2x-y 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 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