lim [x-->0,y-->0] xy/(√(2-e^(xy))-1)
分母有理化
=lim [x-->0,y-->0] xy(√(2-e^(xy))+1)/(2-e^(xy)-1)
=lim [x-->0,y-->0] xy(√(2-e^(xy))+1)/(1-e^(xy))
分母用等价无穷小代换
=lim [x-->0,y-->0] -xy(√(2-e^(xy))+1)/(xy)
=lim [x-->0,y-->0] -(√(2-e^(xy))+1)
=-2
lim [x-->0,y-->0] xy/(√(2-e^(xy))-1)
分母有理化
=lim [x-->0,y-->0] xy(√(2-e^(xy))+1)/(2-e^(xy)-1)
=lim [x-->0,y-->0] xy(√(2-e^(xy))+1)/(1-e^(xy))
分母用等价无穷小代换
=lim [x-->0,y-->0] -xy(√(2-e^(xy))+1)/(xy)
=lim [x-->0,y-->0] -(√(2-e^(xy))+1)
=-2