1
lim x→0y→2 sin(xy)/x
=lim x→0y→2 (xy)/x
=lim x→0y→2 y
= 2
2
lim x→0y→0 (2-√（xy+4）)/xy
= lim x→0y→0 (4-（xy+4）)/[(xy)·(2+√（xy+4）)]
= lim x→0y→0 -（xy）/[(xy)·(2+√（xy+4）)]
= lim x→0y→0 -1/[(2+√（xy+4）)]
= -1/43.lim x→0y→0(x^2y)/(x^3-y^3)4.limx→0y→1xy*sin(1/(x^2+y^2))帮助看看，谢谢。3.令y=kx,则原式=lim x→0(kx^3)/(x^3-k^3·x^3)=k/(1-k^3)随着k值变化极限值也发生变化，因此极限不存在4.=0，没啥说的