# Thread: completing the square

1. ## completing the square

Solve 2x sqaured minus negative 4x minus 1 is equal to zero, so 2x^2-4x-1=0, by completing the square. Express in simplest radical form, and could someone show me how to check the answer?

2. Originally Posted by mcinnes
Solve 2x sqaured minus negative 4x minus 1 is equal to zero, so 2x^2-4x-1=0, by completing the square. Express in simplest radical form, and could someone show me how to check the answer?
$\displaystyle 2x^2 - 4x - 1 = 0$

$\displaystyle x^2 - 2x = \frac{1}{2}$

$\displaystyle x^2 - 2x + 1 = \frac{1}{2} + 1$

$\displaystyle (x - 1)^2 = \frac{3}{2}$

$\displaystyle x - 1 = \pm \sqrt{\frac{3}{2}}$

$\displaystyle x = 1 \pm \sqrt{\frac{3}{2}}$

EDIT: For a further explanation: http://www.purplemath.com/modules/sqrquad.htm