Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 4 - Section 4.5 - Exponential and Logarithmic Functions - 4.5 Exercises - Page 369: 79

Answer

$x\in(2,4)\cup(7,9)$

Work Step by Step

First of all, in order for the inequality to be defined the logarithms must be defined (arguments must be positive): $x-2>0\qquad and\qquad 9-x>0$ $x>2\qquad and\qquad x<9$ $x\in(2,9)\qquad (*)$ ... on the LHS, apply rule: $\log_{a}(AB)=\log_{a}A+\log_{a}B$ ... on the RHS, $1=\log 10$ $\log[(x-2)(9-x)]0$ Factor the trinomial. Two factors of 28 whose sum is -11... $-7$ and $-4$ $(x-4)(x-7)>0$ The LHS would be graphed as a parabola turning upward, with 4 and 7 as zeros. (see graph below) The graph is above the x axis for $x<4$ and $x>7$. Finally, because of (*) ,$x\in(2,9),$ $x\in(2,4)\cup(7,9)$ is the solution to the inequality.
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