x,y趋近于0,lim(xy/(x+y))=lim(1/(1/x+1/y))=0错哪里了?我知道要令y=x,y=x^2-x,但是请问lim(xy/(x+y))=lim(1/(1/x+1/y))=0的做法错哪里了?

x,y趋近于0,lim(xy/(x+y))=lim(1/(1/x+1/y))=0错哪里了?我知道要令y=x,y=x^2-x,但是请问lim(xy/(x+y))=lim(1/(1/x+1/y))=0的做法错哪里了?
x,y趋近于0,lim(xy/(x+y))=lim(1/(1/x+1/y))=0错哪里了?
我知道要令y=x,y=x^2-x,但是请问lim(xy/(x+y))=lim(1/(1/x+1/y))=0的做法错哪里了?

x,y趋近于0,lim(xy/(x+y))=lim(1/(1/x+1/y))=0错哪里了?我知道要令y=x,y=x^2-x,但是请问lim(xy/(x+y))=lim(1/(1/x+1/y))=0的做法错哪里了?
求极限时,如果代入后分母是零,肯定是不能直接代入的.
lim(x,y→0),1/x；1/y,不能直接把0代入得出无穷大,这一步是错的.