completing the square

• Nov 18th 2008, 08:56 AM
mcinnes
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?
• Nov 18th 2008, 10:39 AM
janvdl
Quote:

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?

$2x^2 - 4x - 1 = 0$

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

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

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

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

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

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