Calculus 8th Edition

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

Chapter 1 - Functions and Limits - 1.8 Continuity - 1.8 Exercises - Page 93: 54

Answer

$f(2)≈ 0.414$, $f(3)≈ −0.601.$ There is a root of the equation $\frac{2}{3} − x + \sqrt x= 0,$ or $\frac{2}{x} = x − \sqrt x,$ in the interval $(2, 3)$.

Work Step by Step

Given: $\frac{2}{x} = x − \sqrt x$. The given equation is equivalent to the equation $\frac{2}{x}- x + \sqrt x = 0$. $f(x)=\frac{2}{x} = x − \sqrt x$ is continuous on the interval [2, 3], $f(2) = \frac{2}{2} − 2 + \sqrt 2 $ $= 1 − 2 + \sqrt 2 $ $=-1+1.414$ $f(2)≈ 0.414$, and $f(3) =\frac{ 2}{3} -3 + \sqrt 3$ $=\frac{2-9+3\sqrt 3}{3}$ $=\frac{-7+3(1.732)}{3}$ $=\frac{-7+5.196}{3}$ $=\frac{-1.804}{3}$ $f(3)≈ −0.601.$ Since $f(2) > 0 >f(3),$ there is a number $c$ in $(2, 3)$ such that $f(c)=0$ by the Intermediate Value Theorem. Thus, there is a root of the equation $\frac{2}{3} − x + \sqrt x= 0,$ or $\frac{2}{x} = x − \sqrt x,$ in the interval $(2, 3)$.
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