Big Ideas Math - Algebra 1, A Common Core Curriculum

Published by Big Ideas Learning LLC
ISBN 10: 978-1-60840-838-2
ISBN 13: 978-1-60840-838-2

Chapter 9 - Solving Quadratic Equations - 9.5 - Solving Quadratic Equations Using the Quadratic Formula - Monitoring Progress - Page 520: 15

Answer

$x=\frac{1+\sqrt{21}}{10}\approx 0.56$ and $x=\frac{1-\sqrt{21}}{10}\approx -0.36$.

Work Step by Step

The given equation is $\Rightarrow 5x^2-x-1=0$ The equation is not easily factorable. So, solve using the Quadratic formula. $\Rightarrow 5x^2-x-1=0$ Quadratic formula. $\Rightarrow x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$ Substitute $5$ for $a,-1$ for $b$ and $-1$ for $c$. $\Rightarrow x=\frac{-(-1)\pm\sqrt{(-1)^2-4(5)(-1)}}{2(5)}$ Simplify. $\Rightarrow x=\frac{1\pm\sqrt{1+20}}{10}$ $\Rightarrow x=\frac{1\pm\sqrt{21}}{10}$ Hence, the solutions are $x=\frac{1+\sqrt{21}}{10}\approx 0.56$ and $x=\frac{1-\sqrt{21}}{10}\approx -0.36$.
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