求极限,x趋于1的,分子是1-根号下x,分母是1-立方根号x
问题描述:
求极限,x趋于1的,分子是1-根号下x,分母是1-立方根号x
答
可以直接用洛必达,分子分母同时求导得:分子:(-1/2)x^(-1/2),分母:(-1/3)x^(-2/3)
最后化简得:(3/2)x^(1/6),然后1代入x可得3/2
答
lim(x->1) [ 1- x^(1/2) ]/[1- x^(1/3) ] (0/0)
=lim(x->1) -(1/2) x^(-1/2) / [-(1/3) x^(-2/3) ]
=(3/2)lim(x->1) x^(1/6)
=3/2
答
方法一:
lim(x→1){[1-x^(1/2)]/[1-x^(1/3)]}
=lim(x→1){[1-x^(3/6)]/[1-x^(2/6)]}
=lim(x→1){[1+x^(1/6)+x^(2/6)]/[1+x^(1/6)]}
=[1+1^(1/6)+1^(2/6)]/[1+1^(1/6)]
=3/2
方法二:利用洛必塔法则.
lim(x→1){[1-x^(1/2)]/[1-x^(1/3)]}
=lim(x→1){[-(1/2)x^(-1/2)]/[-(1/3)x^(-2/3)]}
=[-(1/2)×1^(-1/2)]/[-(1/3)×1^(-2/3)]
=3/2.