Math Problem Statement

prove 2^n > n by induction

Solution

To prove the inequality 2n>n2^n > n for all integers n1n \geq 1 using mathematical induction, we proceed as follows:

Step 1: Base Case

We check if the inequality holds for n=1n = 1.

21=2and1=1.2^1 = 2 \quad \text{and} \quad 1 = 1.

Clearly, 2>12 > 1, so the base case holds.

Step 2: Inductive Hypothesis

Assume that the inequality 2k>k2^k > k holds for some arbitrary positive integer kk. That is, we assume:

2k>k.2^k > k.

Step 3: Inductive Step

We need to show that 2k+1>k+12^{k+1} > k+1, assuming the inductive hypothesis 2k>k2^k > k.

Now, consider:

2k+1=22k.2^{k+1} = 2 \cdot 2^k.

Using the inductive hypothesis, we know that 2k>k2^k > k. Thus, multiplying both sides of this inequality by 2 gives:

2k+1=22k>2k.2^{k+1} = 2 \cdot 2^k > 2 \cdot k.

Therefore, we need to show that:

2kk+1.2 \cdot k \geq k + 1.

Simplifying the inequality:

2kk+1k1.2k \geq k + 1 \quad \Longleftrightarrow \quad k \geq 1.

This is true because k1k \geq 1 for all positive integers kk. Thus, we have shown that:

2k+1>k+1.2^{k+1} > k + 1.

Conclusion:

By mathematical induction, the inequality 2n>n2^n > n holds for all integers n1n \geq 1.


Would you like further clarification on any part of this proof?

Here are five related questions:

  1. How do we prove more complex inequalities using induction?
  2. Can the same approach be used to prove 3n>n23^n > n^2?
  3. What is the significance of base cases in induction?
  4. How do we choose an appropriate inductive hypothesis for different problems?
  5. How does strong induction differ from regular induction?

Tip: Always make sure to clearly state the inductive hypothesis and how it is used in the inductive step.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Mathematical Induction
Inequalities
Exponential Functions

Formulas

2^n > n

Theorems

Principle of Mathematical Induction

Suitable Grade Level

Grades 9-12