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Q.Prove that 2n>n2^n > n for all positive integer.

Bihar BsebBihar Board Intermediate 1st Year 2023Subjective· 2mImportance★★★★★
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2n>n2^n>n for all positive integers, by induction.

Let P(n):2n>nP(n):2^n>n (NCERT Class 11 Principle of Mathematical Induction).

Base: P(1):21=2>1P(1):2^1=2>1 ✓.

Inductive step: Assume P(k)P(k) true, i.e. 2k>k2^k>k. Then

2k+1=2⋅2k>2k=k+k≥k+1(since k≥1).2^{k+1}=2\cdot 2^k>2k=k+k\ge k+1\quad(\text{since }k\ge1).

So 2k+1>k+12^{k+1}>k+1, i.e. P(k+1)P(k+1) holds.

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