Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 1 - Functions and Limits - Principles of Problem Solving - Problems - Page 104: 23

Answer

$\dfrac{3}{4}$

Work Step by Step

Let's use the limit property and expand the brackets $\lim\limits_{x \to a}(f(x)+g(x))=\lim\limits_{x \to a}f(x)+\lim\limits_{x \to a}g(x)=f(a)+g(a)=2;$ At the same time $\lim\limits_{x \to a}(f(x)-g(x))=\lim\limits_{x \to a}f(x)\lim\limits_{x \to a}g(x)=f(a)-g(a)=1;$ We have a system of equations $$ \begin{cases} f(a)+g(a)=2\\ f(a)-g(a)=1\\ \end{cases} $$ Let's add two equations $f(a)+g(a)+f(a)-g(a)=2+1$ $2f(a)=3$ or $f(a)=\frac{3}{2}$ Let's subtract the second equations from the first $f(a)+g(a)-(f(a)-g(a))=2-1$ $f(a)+g(a)-f(a)+g(a)=1$ $2g(a)=1$ or $g(a)=\frac{1}{2}$ Now it's easy to find the answer $\lim\limits_{x \to a}(f(x)g(x))=\lim\limits_{x \to a}f(x)\lim\limits_{x \to a}g(x)=f(a)g(a)=\frac{3}{2}\cdot\frac{1}{2}=\frac{3}{4}$
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