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 368: 48

Answer

$x=-\dfrac{1}{2}\pm\dfrac{\sqrt{5}}{2}$

Work Step by Step

$x^{2}e^{x}+xe^{x}-e^{x}=0$ Take out common factor $e^{x}$: $e^{x}(x^{2}+x-1)=0$ Set both factors equal to $0$ and solve each individual equation: $e^{x}=0$ No value of $x$ makes this first equation true. It has no solution. Move on to the second one: $x^{2}+x-1=0$ Use the quadratic formula to solve this second equation. The formula is $x=\dfrac{-b\pm\sqrt{b^{2}-4ac}}{2a}$. For this equation, $a=1$, $b=1$ and $c=-1$. Substitute the known values into the formula and simplify: $x=\dfrac{-1\pm\sqrt{1^{2}-4(1)(-1)}}{2(1)}=\dfrac{-1\pm\sqrt{1+4}}{2}=\dfrac{-1\pm\sqrt{5}}{2}=...$ $...=-\dfrac{1}{2}\pm\dfrac{\sqrt{5}}{2}$ The solutions are: $x=-\dfrac{1}{2}\pm\dfrac{\sqrt{5}}{2}$
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