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Q.Using the principle of mathematical induction prove that 12+14+18+⋯+12n=1−12n\dfrac{1}{2} + \dfrac{1}{4} + \dfrac{1}{8} + \cdots + \dfrac{1}{2^n} = 1 - \dfrac{1}{2^n}.

Meghalaya MboseMBOSE Meghalaya 11th Board 2022Subjective· 6mImportance★★★★★
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The identity is proven by the principle of mathematical induction (PMI), checking a base case and an inductive step.

Let P(n)P(n): 12+14+18+⋯+12n=1−12n\dfrac12+\dfrac14+\dfrac18+\cdots+\dfrac1{2^n} = 1-\dfrac1{2^n}.

Base case (n=1n=1): LHS =12=\dfrac12; RHS =1−12=12=1-\dfrac12=\dfrac12. So P(1)P(1) is true.

Inductive step: Assume P(k)P(k) is true, i.e.

12+14+⋯+12k=1−12k.\dfrac12+\dfrac14+\cdots+\dfrac1{2^k} = 1-\dfrac1{2^k}.

We show P(k+1)P(k+1) holds. Add 12k+1\dfrac{1}{2^{k+1}} to both sides: …

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