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 330: 10

Answer

a) 1/2, 2/3 and n/n+1 b) BASIC STEP: it is given that the n is positive integer then, put n=1 1/2 =1/1+1 =1/2 (The left-hand side of this equation is 1/2 because 1/2 is the sum of the first a positive integer. The right-hand side is found by substituting 1/2 for n in n/n+1 INDUCTIVE STEP: For the inductive hypothesis we assume that $P(k $) $1/1.2+1/2.3+... +1/k (k+1) = k/k+1$ Under the assumption, it must be show that$ P(k+1)$ is true, namely, that. $1/1.2+1/2.3+... +1/(k+1) (k+2) = k+1/k+2$ When we add 1/(k+1) (k+2) to both side of the equation in P(K), we obtain. $1/1.2+1/2.3+... +1/k (k+1) + 1/(k+1) (k+2) = k/k+1 + 1/(k+1) (k+2) $ [By the inductive hypothesis] = $k(k+2) +1/(k+1) (k+2)$ =$k2+2k+1/(k+1) (k+2)$ =$k+1/k+2$ We have completed the basis step and the inductive step, so by mathematical inductive we know that P(n) is true for all positive integers n. That is, we have proven that. $1/1.2+1/2.3+... +1/n (n+1) $=$ n/n+1$

Work Step by Step

a) 1/2, 2/3 and n/n+1 b) BASIC STEP: it is given that the n is positive integer then, put n=1 1/2 =1/1+1 =1/2 (The left-hand side of this equation is 1/2 because 1/2 is the sum of the first a positive integer. The right-hand side is found by substituting 1/2 for n in n/n+1 INDUCTIVE STEP: For the inductive hypothesis we assume that P(k) 1/1.2+1/2.3+... +1/k (k+1) = k/k+1 Under the assumption, it must be show that P(k+1) is true, namely, that. 1/1.2+1/2.3+... +1/(k+1) (k+2) = k+1/k+2 When we add 1/(k+1) (k+2) to both side of the equation in P(K), we obtain. 1/1.2+1/2.3+... +1/k (k+1) + 1/(k+1) (k+2) = k/k+1 + 1/(k+1) (k+2) [By the inductive hypothesis] = k(k+2) +1/(k+1) (k+2) =k2+2k+1/(k+1) (k+2) =k+1/k+2 We have completed the basis step and the inductive step, so by mathematical inductive we know that P(n) is true for all positive integers n. That is, we have proven that. 1/1.2+1/2.3+... +1/n (n+1) = n/n+1
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