若｛x=1,y=-1和｛x=2,y=2都是二元一次方程组mx+ny=-4的解,判断｛x=3y=4是否也是此方程的解,说明理由

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 若x.y满足x+=4和x-y=2,求xy分之2x-y+1除以-x分之y+y分之x的值 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x 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 若关于x y的二元一次方程组2x+y=2m-1 x+2y=m满足x+y>0和x-y 若x,y∈R,(x+y)^2i+6i-x=-y+5(x+y)i-1,求x和y的值 (x-2y)(x+y)-2x(-2x-3y)+6x(-x-y),其中x=-1,y=2要讲解和答题 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 2x+4y=3 -3x-2y=1 ..求x和y 2x+y=1,25x+2y=-40,求x和y? 解方程组,(x+y)^2-3(x+y)=0和x-y=1 (2x-2y)/3-(x-y)=-1和6(x+y)-4(2x-y)=16