# surd maths question :S

• Jan 8th 2010, 09:35 AM
bubbylgirl
surd maths question :S
Hey, i've been doing a maths practice paper for revision but i've come across a question i don't understand. Can anyone help me??

Find the exact roots of the equation 2x(squared)+8x-5=0 giving your answers in their simplest form.

The answer is -2(plus or minus)1/2 (square root) 26
but i just keep getting -2(plus or minus) (square root) 24
:S i don't know where i'm going wrong

xx
• Jan 8th 2010, 10:06 AM
masters
Quote:

Originally Posted by bubbylgirl
Hey, i've been doing a maths practice paper for revision but i've come across a question i don't understand. Can anyone help me??

Find the exact roots of the equation 2x(squared)+8x-5=0 giving your answers in their simplest form.

The answer is -2(plus or minus)1/2 (square root) 26
but i just keep getting -2(plus or minus) (square root) 24
:S i don't know where i'm going wrong

xx

Hi bubblygirl,

You probably made a simple error somewhere.

$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$

$x=\frac{-8\pm\sqrt{8^2-4(2)(-5)}}{2(2)}$

$x=\frac{-8\pm\sqrt{104}}{4}$

$x=\frac{-8\pm\sqrt{4\cdot26}}{4}$

$x=\frac{-8\pm2\sqrt{26}}{4}$

$x=\frac{-8}{4}\pm\frac{2}{4}\sqrt{26}$

$x=-2\pm\frac{1}{2}\sqrt{26}$
• Jan 8th 2010, 10:10 AM
bubbylgirl
Quote:

Originally Posted by masters
Hi bubblygirl,

You probably made a simple error somewhere.

$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$

$x=\frac{-8\pm\sqrt{8^2-4(2)(-5)}}{2(2)}$

$x=\frac{-8\pm\sqrt{104}}{4}$

$x=\frac{-8\pm\sqrt{4\cdot26}}{4}$

$x=\frac{-8\pm2\sqrt{26}}{4}$

$x=\frac{-8}{4}\pm\frac{2}{4}\sqrt{26}$

$x=-2\pm\frac{1}{2}\sqrt{26}$

ohhhhh i forgot that its minus 5 and a minus X a minus is a plus
thanks sooo much