# How do you solve 3x^2 + 11x – 20 = 0 by completing the square?

Jul 3, 2015

Solve y = 3x^2 + 11x - 20 = 0

#### Explanation:

y = 3(x^2 + 11x/3) - 20/3 = 0
(x^2 + 11x/3 + 121/36) - 121/36 = 20/3
(x + 11/6)^2 = 20/3 + 121/36 = 361/36
(x + 11/6)^2 = 361/36 =
$\left(x + \frac{11}{6}\right) = \pm \frac{19}{6}$

$x = - \frac{11}{6} + \frac{19}{6} = \frac{8}{6} = \frac{4}{3}$

$x = - \frac{11}{6} - \frac{19}{6} = - \frac{30}{6} = - 5$