Discrete Mathematics and Its Applications, Seventh Edition

Published by McGraw-Hill Education
ISBN 10: 0073383090
ISBN 13: 978-0-07338-309-5

Chapter 5 - Section 5.1 - Mathematical Induction - Exercises - Page 332: 57

Answer

Proof by Induction

Work Step by Step

The Base Case: The $n$ is a positive integer. So the smallest value it can assume is 1 which we take to be our base case. For $n=1$, f(x) = $x^1$ LHS = $f^{'}(x)$ = $(x)^{'}$ = 1 as is known that the derivative of the identity function is the constant unit function. And RHS = $1 \times x^0$ = 1 Therefore, LHS = RHS Inductive Hypothesis: Let's say for a given n = k, $(x^k)^{'}$ = $k \times x^{k-1}$ ........................ (1) So for k+1, LHS = $(x^{k+1})^{'}$ = $(x\times x^k)^{'}$ By product rule, LHS = $x\times (x^k)^{'} + x^{'} \times x^k $ By (1), LHS = $x\times (k \times x^{k-1} ) + 1 \times x^k $ or $LHS = k \times x^k + x^k = (k+1) \times x^k$ = RHS Thus, by the domino effect of the principle of induction, the assertion is proved.
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