Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 7 - Section 7.3 - Partial Fractions - Exercise Set - Page 842: 51


The simplified solution is $\frac{1}{x}-\frac{1}{x+1}$ and its sum is $\frac{99}{100}$.

Work Step by Step

Let us consider the rational expression. $\begin{align} & \frac{1}{x\left( x+1 \right)}=\frac{A}{x}+\frac{B}{x+1} \\ & =\frac{A\left( x+1 \right)+Bx}{x\left( x+1 \right)} \end{align}$ $1=A\left( x+1 \right)+Bx$ (I) Substitute the value of $x=-1$ in the equation (I), $\begin{align} & 1=B\left( -1 \right) \\ & B=-1 \end{align}$ Again, putting the value of $x=0$ in the equation (I), $\begin{align} & 1=A\left( 1 \right) \\ & A=1 \end{align}$ Therefore, $\frac{1}{x\left( x+1 \right)}=\frac{1}{x}-\frac{1}{x+1}$ is the simplified form of the result By using the above result to find the sum of the series, $\begin{align} & \frac{1}{1\cdot 2}+\frac{1}{2\cdot 3}+\frac{1}{3\cdot 4}+\cdots +\frac{1}{99\cdot 100} \\ & =\left( \frac{1}{1}-\frac{1}{2} \right)+\left( \frac{1}{2}-\frac{1}{3} \right)+\left( \frac{1}{3}-\frac{1}{4} \right)+\cdots +\left( \frac{1}{99}-\frac{1}{100} \right) \\ & =\frac{1}{1}-\frac{1}{100} \\ & =\frac{99}{100} \end{align}$ Thus, the sum is $\frac{99}{100}$.
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