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Important Result (Comparison) - Practice Questions & MCQ

Edited By admin | Updated on Sep 18, 2023 18:34 AM | #JEE Main

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  • 4 Questions around this concept.

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If y=(x)^{3x} for x>2, which of the following is true?

The value of the natural numbers n such that the inequality  2^n>2 n+1  is valid:

Concepts Covered - 1

Important Result (Comparison)

Important Result (Comparison)

    2\leq\left ( 1+\frac{1}{n} \right )^n<3,\;\;\;\;\;n\in\mathbb{N}

Proof:

Expand, \\ \left ( 1+\frac{1}{n} \right )^n \text{using binomial theorem} \\\\

\begin{aligned}\left(1+\frac{1}{n}\right)^{n} &=1+n \frac{1}{n}+\frac{n(n-1)}{2 !} \frac{1}{n^{2}}+\frac{n(n-1)(n-2)}{3 !} \frac{1}{n^{3}}+\cdots+\frac{n(n-1)(n-2) \cdots[n-(n-1)]}{n !} \frac{1}{n^{n}} \\&={1+1+\frac{1}{2 !}\left(1-\frac{1}{n}\right)+\frac{1}{3 !}\left(1-\frac{1}{n}\right)\left(1-\frac{2}{n}\right)} {+\cdots+\frac{1}{n !}\left(1-\frac{1}{n}\right)\left(1-\frac{2}{n}\right) \dots\left(1-\frac{n-1}{n}\right)}\\&{<1+1+\frac{1}{2 !}+\frac{1}{3 !}+\cdots+\frac{1}{n !}}\\&{<1+1+\frac{1}{2}+\frac{1}{2^{2}}+\frac{1}{2^{3}}+\cdots+\frac{1}{2^{n-1}}}=1+1 \frac{\left\{1-\left(\frac{1}{2}\right)^{n}\right\}}{1-\frac{1}{2}}=1+2\left\{1-\left(\frac{1}{2}\right)^{n}\right\}=3-\frac{1}{2^{n-1}}\end{aligned}

Hence, from above

2\leq\left ( 1+\frac{1}{n} \right )^n<3,\;\;n\geq1

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Important Result (Comparison)

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