The Student Room Group

n^n

We know o^n = 0 for all n <> 0

We also know n^0 = 1 for all n <> 0

But why is n^n undefined for n = 0 but in the limit n^n = 1?

Scroll to see replies

Reply 1
Original post by lotsofq
We know o^n = 0 for all n <> 0

We also know n^0 = 1 for all n <> 0

But why is n^n undefined for n = 0 but in the limit n^n = 1?


Limits do not prove equality: it only shows that as it gets closer to 0, it's tending to 1.

0^0 = 0^1 * 0^-1

However 0^-1 is not defined.
(edited 12 years ago)
Reply 2
2^0=1
1^0=1
0^0=1

0^2=0
0^1=0
0^0=0

Contradiction.
I thought the limit didn't exist
Reply 4
Original post by ben-smith
I thought the limit didn't exist


It does.

Consider the limit as x->0+ x^x = lim x->0+ e^(xlogx)
Reply 5
I know the answer, lim n->0 (n^n) = 1 but just don't know why 0^0 is undefined.
Original post by f1mad
It does.

Consider the limit as x->0+ x^x = lim x->0+ e^(xlogx)


That's the limit from above. I just mean the limit.
Reply 7
Original post by lotsofq
I know the answer, lim n->0 (n^n) = 1 but just don't know why 0^0 is undefined.


I suppose it's so you can't do crazy stuff like 1=00=010=0100=01=01=0^0=0^{1\cdot 0}=0^10^0=0\cdot 1 = 0
Reply 8
Original post by ttoby
I suppose it's so you can't do crazy stuff like 1=00=010=0100=01=01=0^0=0^{1\cdot 0}=0^10^0=0\cdot 1 = 0


Surely your 0^0 = 0^(1.0) doesn't make sense?
Reply 9
Original post by lotsofq
I know the answer, lim n->0 (n^n) = 1 but just don't know why 0^0 is undefined.


The two-variable limit x^y doesn't exist as (x,y) -> (0,0).

the one variable limit x^x does exist as x -> 0.
Reply 10
Original post by ben-smith
That's the limit from above. I just mean the limit.


If you do the series expansion of e^(xlogx) and then let x->0, you'll be left with 1.
Original post by f1mad
If you do the series expansion of e^(xlogx) and then let x->0, you'll be left with 1.


OK, I'll take your word for it. Infinite series don't always converge so I guess one would have to deal with that issue :s-smilie:
Reply 12
Original post by lotsofq
Surely your 0^0 = 0^(1.0) doesn't make sense?


1×0=01\times 0=0 so I can replace 0 with 1×01\times 0. Of course all this doesn't make sense anyway since 0^0 isn't defined.
To find the limit of x^x as x->0 (from above), first find the limit of ln(x^x) = x ln x. If this limit exists, then since exp is continuous, lim exp(ln(x^x)) -> exp(lim ln(x^x)).
Reply 14
Original post by ben-smith
OK, I'll take your word for it. Infinite series don't always converge so I guess one would have to deal with that issue :s-smilie:


I'm pretty sure this limit is only from above.

If one substitutes (x)x=1(x)x\displaystyle (-x)^{-x} = \frac{1}{(-x)^x} and considers this limit from above, given ϵ\epsilon, every now and then you come across a rational in 0<x<δ(ϵ)0 < x < \delta(\epsilon).
(edited 12 years ago)
Reply 16
Original post by ttoby
I suppose it's so you can't do crazy stuff like 1=00=010=0100=01=01=0^0=0^{1\cdot 0}=0^10^0=0\cdot 1 = 0


Since when could you do a^(b*c)=(a^b)*(a^c)?
Reply 17
Original post by james22
Since when could you do a^(b*c)=(a^b)*(a^c)?


Yeah... you got me. Double facepalm etc etc.
Reply 18
If I'm doing set theory then I argue that 00=10^0=1, since we can define aba^b to be the cardinality of the set of functions BAB \to A where A=a\left| A \right| = a and B=b\left| B \right| = b. When A=B=A=B=\varnothing, this set consists only of the empty function, so its cardinality is 1.

If I'm doing analysis then I argue that 000^0 is undefined, since for instance limx0x0=1\lim_{x \to 0} x^0 = 1 but limx00x=0\lim_{x \to 0} 0^{\left|x\right|} = 0.
(edited 12 years ago)
Original post by nuodai
If I'm doing set theory then I argue that 00=10^0=1, since we can define aba^b to be the cardinality of the set of functions BAB \to A where A=a\left| A \right| = a and B=b\left| B \right| = b. When A=B=A=B=\varnothing, this set consists only of the empty function, so its cardinality is 1.

If I'm doing analysis then I argue that 000^0 is undefined, since for instance limx0x0=1\lim_{x \to 0} x^0 = 1 but limx00x=0\lim_{x \to 0} 0^{\left|x\right|} = 0.


But I thought the beauty of maths is that there is no ambiguity, with there ever only being one universal answer to a problem or are we delving into the higher echelons?

Quick Reply

Latest