r² – rn+1 5. Let r +1 be a real number. Use induction to show that r* for all 1-r k-2 ne Z+ with n > 2.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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### Problem Statement

**Problem 5**: 
Let \( r \neq 1 \) be a real number. Use induction to show that 
\[ \sum_{k=2}^{n} r^k = \frac{r^2 - r^{n+1}}{1 - r} \]
for all \( n \in \mathbb{Z}^+ \) with \( n \geq 2 \). 

### Explanation

To tackle this problem, follow these steps:

1. **Base Case**: Start with the smallest value of \( n \), which is 2, and verify that the formula holds.

2. **Inductive Hypothesis**: Assume that the formula holds for some arbitrary positive integer \( n \), i.e., assume
   \[ \sum_{k=2}^{n} r^k = \frac{r^2 - r^{n+1}}{1 - r} \]

3. **Inductive Step**: Show that if the formula holds for \( n \), then it also holds for \( n + 1 \), i.e., show that
   \[ \sum_{k=2}^{n+1} r^k = \frac{r^2 - r^{(n+1)+1}}{1 - r} \]

By establishing these steps through mathematical induction, the given formula can be proven for all \( n \geq 2 \).
Transcribed Image Text:### Problem Statement **Problem 5**: Let \( r \neq 1 \) be a real number. Use induction to show that \[ \sum_{k=2}^{n} r^k = \frac{r^2 - r^{n+1}}{1 - r} \] for all \( n \in \mathbb{Z}^+ \) with \( n \geq 2 \). ### Explanation To tackle this problem, follow these steps: 1. **Base Case**: Start with the smallest value of \( n \), which is 2, and verify that the formula holds. 2. **Inductive Hypothesis**: Assume that the formula holds for some arbitrary positive integer \( n \), i.e., assume \[ \sum_{k=2}^{n} r^k = \frac{r^2 - r^{n+1}}{1 - r} \] 3. **Inductive Step**: Show that if the formula holds for \( n \), then it also holds for \( n + 1 \), i.e., show that \[ \sum_{k=2}^{n+1} r^k = \frac{r^2 - r^{(n+1)+1}}{1 - r} \] By establishing these steps through mathematical induction, the given formula can be proven for all \( n \geq 2 \).
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