View Full Version : how would you prove this little inequality?
stunner5000pt
Mar2-04, 10:14 PM
i'm stuck trying to prove this little inequality:
(1+ 1/n)^n <= e <= (1+1/n)^n+1
is there a way to prove this without without resorting to power series for e (because we're not allowed to, and we don't know this yet) and also note that n is a natural number, (positive integer).
cookiemonster
Mar2-04, 10:47 PM
Here's a hint:
\lim_{n \to \infty} \Big( 1 + \frac{1}{n} \Big)^n = e
cookiemonster
stunner5000pt
Mar2-04, 10:59 PM
ok i know tha already i just dont know how to prove it give me hint on hwo to prove it
cookiemonster
Mar2-04, 11:39 PM
Just how formally do you want to prove it?
It's pretty easy to notice that for n<\infty, the left side is less than e. When n = \infty, it is exactly equal to e.
The same holds true for the right side, except that it's always greater than e except when n = \infty.
cookiemonster
matt grime
Mar3-04, 04:53 AM
You do it by power series for (1+x)^n valid when |x|<1 (ie x=1/n)
Originally posted by stunner5000pt
i'm stuck trying to prove this little inequality:
(1+ 1/n)^n <= e <= (1+1/n)^n+1
is there a way to prove this without without resorting to power series for e (because we're not allowed to, and we don't know this yet) and also note that n is a natural number, (positive integer).
Why can you not just reason that (1+1/n)^n has to be less than (1+1/n)^n * (1+1/n), as, until n => infinity, 1+1/n will always be a positive value above * a positive value that will always make the right hand larger.
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