1/[(1/x)+(1/y)]=24,[1-(20/x)]/(y/1)=40头大的用图气死我了

y'/y=1/x y'-(1/x)y=xe^-x 概率密度f(x,y)=24y(1-x-y),求P{X0,y>0,x+y y(x+y)+(x-y)²-（x+y）（x-y）,其中x=-1/3,y=3 （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 x>=1,x-y y=x-1(x 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都是自然数,且x(x-u)-y(y-x)+12,求x.y得值快1且x(x-y)-y(y-x)=12 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 先化简再求值; 解方程组 x(x-y)-y(x+y)+2xy 其中x=2 ,y=-22.x[x-x(x-1)],其中x=-2解方程组4x+3y=12x-y=32.y+1=2x 4x-y=2 3.2x+2y=0 2x-y+24=0 [(y*y*y-y)/(xy+1)*(xy+1)-(x+y)*(x+y)]/[(x+y)*y/(x+1)]其中x=-11,y=1/12,化简再求值. y=[x-1], 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 {3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1 常微分方程y'=(x+y)ln(x+y)-1