lim(x,y)-(0,0)=根号下(xy+9)-3/xy

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lim(x,y)-(0,0)=根号下(xy+9)-3/xy
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lim(x,y)-(0,0)=根号下(xy+9)-3/xy
lim(x,y)-(0,0)=根号下(xy+9)-3/xy

lim(x,y)-(0,0)=根号下(xy+9)-3/xy
=lim(x,y)-(0,0) [(xy+9)-9]/[xy·(根号下(xy+9) +3)]
=lim(x,y)-(0,0) (xy)/[xy·(根号下(xy+9) +3)]
=lim(x,y)-(0,0) 1/[根号下(xy+9) +3]
= 1/6

lim(x,y)-(0,0)=根号下(xy+9)-3/xy=[根号下(xy+9)-3]*[根号下(xy+9)+3]/{[根号下(xy+9)+3]*xy}
=1/[根号下(xy+9)+3]=1/6

分子有理化
分子分母同乘以(根号下(xy+9)+3)
得1/(根号下(xy+9)+3)
得极限值为1/6