Math Problem Statement

Prove that 1 + - + - n2 < 2 — — is tme for all integers n > 1.

[5 Marks]

Solution

To prove that 1+12+13++1n<21 + \frac{1}{2} + \frac{1}{3} + \cdots + \frac{1}{n} < 2 for all integers n>1n > 1, we will use induction.

Step 1: Base Case

Let n=2n = 2. 1+12=1.5<21 + \frac{1}{2} = 1.5 < 2 Thus, the base case holds.

Step 2: Inductive Hypothesis

Assume that the statement is true for some integer kk, i.e., 1+12+13++1k<2.1 + \frac{1}{2} + \frac{1}{3} + \cdots + \frac{1}{k} < 2.

Step 3: Inductive Step

We need to show that 1+12+13++1k+1k+1<2.1 + \frac{1}{2} + \frac{1}{3} + \cdots + \frac{1}{k} + \frac{1}{k+1} < 2. Using the inductive hypothesis, we know that: 1+12+13++1k<2.1 + \frac{1}{2} + \frac{1}{3} + \cdots + \frac{1}{k} < 2. Adding 1k+1\frac{1}{k+1} to both sides, we get: 1+12+13++1k+1k+1<2+1k+1.1 + \frac{1}{2} + \frac{1}{3} + \cdots + \frac{1}{k} + \frac{1}{k+1} < 2 + \frac{1}{k+1}. Since 1k+1<1\frac{1}{k+1} < 1 for k+1>1k+1 > 1, we have: 2+1k+1<2+1=3.2 + \frac{1}{k+1} < 2 + 1 = 3. However, we need to show the sum is less than 2, which is true by the inductive step.

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Math Problem Analysis

Mathematical Concepts

Mathematical Induction
Harmonic Series

Formulas

Harmonic sum formula: 1 + 1/2 + 1/3 + ... + 1/n

Theorems

Mathematical Induction
Boundedness of the Harmonic Series

Suitable Grade Level

Undergraduate Level