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Math Help - Euler's number

  1. #1
    a.a
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    Arrow Euler's number

    The number is defined as the limit of (1+1/n)^n as n approched infinity.
    My question is why is that limit the number e. If you evaluate it useing the subsistutaion method, you get the limit is 1.

    E is also defined as the limit of (1+n)^(1/n) as n approaches 0. Using the substitution method isn't this limit also 1?
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  2. #2
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    Quote Originally Posted by a.a View Post
    My question is why is that limit the number e. If you evaluate it useing the subsistutaion method, you get the limit is 1.
    Could you please shows that substitution method and show us how the limit evaluates to 1?

    On the other hand \left(1 + \frac1{n}\right)^n = 1 + {n \choose 1} \frac1{n} + {n \choose 2} \frac1{n^2} + ....

    Thus \forall n \in \mathbb{N}\, , \, \left(1 + \frac1{n} \right)^n > 1 + {n \choose 1} \frac1{n}

    Which means \forall n \in \mathbb{N}\, ,\,  \left(1 + \frac1{n}\right)^n > 2

    This means for all natural numbers the expression is always greater than 2... How can the limit be 1 then?
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  3. #3
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    Quote Originally Posted by Isomorphism View Post
    Could you please shows that substitution method and show us how the limit evaluates to 1?
    lim (1+ 1/n)^n as n approaches infinity
    = (1+ 0)^enfinity
    = 1

    lim (1+ n) ^(1/n) as n approaches 0
    = (1+0)^enfinity
    = 1
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  4. #4
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    1^{\infty} is an indeterminate form just like 0^{0} is where the limit depends on the functions you have in place of 1, 0, or infinity. 1^{\text{anything}} isn't always 1. For example:
    \lim_{x \to 0} \cos (x)^{\frac{1}{x^{2}}} = \left[1^{\infty}\right] = e^{-\frac{1}{2}}

    How?
    \lim_{x \to 0} \cos (x)^{\frac{1}{x^{2}}} = e^{\lim_{x \to 0} \ln \cos x^{1/x^{2}}}

    Looking at the exponent:
    \lim_{x \to 0} \ln \cos x^{1/x^{2}} = \lim_{x \to 0} \frac{\ln \cos x}{x^{2}} = \left[\frac{0}{0}\right]
    = \lim_{x \to 0} \frac{-\tan x}{2x} = \left[\frac{0}{0}\right]
    = \lim_{x \to 0} \frac{-sec^{2} x}{2} = - \frac{1}{2}

    Going back to the original limit, we see that:
    \lim_{x \to 0} \cos (x)^{\frac{1}{x^{2}}} = e^{-\frac{1}{2}} \neq {\color{red} 1}
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  5. #5
    Lord of certain Rings
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    Quote Originally Posted by a.a View Post
    lim (1+ 1/n)^n as n approaches infinity
    = (1+ 0)^enfinity
    = 1

    lim (1+ n) ^(1/n) as n approaches 0
    = (1+0)^enfinity
    = 1
    Speaking loosely, 1^{\infty} \neq 1.That is your mistake

    Look at my old post again. I have proved that (1+ 1/n)^n is always greater than 2.
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