A={(x,y)|2x+y=1,x,y是实数}B={（x,y)|a*2x+2y=a,x,y是实数} 若A交B=空集,求a值

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/x-x+y/y-(x+y)(x-y)/y² y/x=2 当A=1,Y=-2时,代数式X-(X+Y)+(X+2Y)-(X+3Y).-(X+99Y)值是( ) 对于(y一撇）y`=y/x(y-1)求导,我求的结果是y``=-y^2-y`x+y/x^2(y-1)^2 怎么不对啊,我的求导过程是：y`x(y-1) - [x(y-1)]` y y`xy-y`x-(y-1+xy`)y -y^2-y`x+yy``=-------------------------=----------------------=-----------------x^2 (y-1 A={(X,Y)|X+Y>=1},B={(X,y)|X^2+y^2=1},B={(X,y)|X^2+y^2 A={(x,y)|2x+y=1,x,y是实数}B={（x,y)|a*2x+2y=a,x,y是实数} 若A交B=空集,求a值 若x+y=4,则多项式1/2(x+y)+4(x-y)-3（x-y）-3/2(x+y)-x+y值是（） （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 A={(x,y)|y=-x^2+mx-1},B={(x,y)|y=3-x,0A={(x,y)|y=-x^2+mx-1},B={(x,y)|y=3-x,0 设A={(x,y)/x+y 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 集合A={（x,y)|y=-x^2+mx-1},B={(x,y)|y=3-x,0 已知集合A={(x,y)|2x-y+2>=0,x-2y+1 设x>0,y>0,a=x+y/1+x+y ,b=x/(1+x)+y/(1+y),则a,b的大小关系是? 设x>0,y>0,A=(x+y)/(1+x+y),B=x/(1+x)+y/(1+y).则A,B的大小关系是? 方程组{ X+Y=1 X-Y=2a }的解满足 {x>0 y 集合{(x,y)}|x/(1+x)+y/(1+y)=(x+y)/(1+x+y)|表示的曲线是?