Question #0f1e0

2 Answers
Dec 29, 2017

#-1#

Explanation:

#lim_(nrarroo)-n^(1/n)#

The #1/n# term will approach #0# as #nrarroo#. Few examples:

#1/2=0.5#
#1/3=0.333...#
#1/5=0.2#
#1/10=0.1#
#1/100 = 0.01#

As you can see, as the denominator gets bigger, it approaches 0.

This means that our question becomes #lim_(nrarroo)-n^0#

Since any number to the power of #0# is #1#, all that is left is the #-# sign and the #1#.

#lim_(nrarroo)-n^0#

#=lim_(nrarroo)-1#

#=-1#

Dec 29, 2017

-1, using #ln# and L'opitals rule

Explanation:

First, lets try plugging in the limit: #-n^(1/n)-> -oo^0#.
This produces an indeterminate form, in other words we can't draw any immediate conclusions from this; we have to do more work.

Whenever we have one function to the power of another (in this case #n# to the #1/n#), it usually helps to let the set the limit equal to some variable #L#, then take then #ln# of both sides, as shown below. We'll leave out the - sign as well for now, just remembering to change the sign of the final answer:

#L=lim_(n->oo)n^(1/n)#
#ln(L)=lim_(n->oo)ln(n^(1/n))# (Side note: we can do this because the ln function is continuous for the region we're interested in)
But by log laws, we can move the index down:
#ln(L)=lim_(n->oo)(1/n)ln(n)#
#ln(L)=lim_(n->oo)ln(n)/n#

Now if we plug in #oo# to the left, we get the form #oo/oo#, and because the numerator and denominator are both continuous functions we get to use L'opitals rule:

#ln(L)=lim_(n->oo)(1/n)/1#
#ln(L)=lim_(n->oo)1/n#
NOW, the right hand side is for sure 0:
#ln(L) = 0#
And we raise both sides to #e#:
#L=e^0=1#

But remember that there was a - sign we left out for convenience, so we put that back in and get our final answer of -1

P.S. I'm assuming you means #-(n^(1/n))# not #(-n)^(1/n)#, because otherwise we wouldn't get any answer at all.

If any of the above things such as L'opitals rule need further explanation, please ask.