# Thread: surd maths question :S

1. ## 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

2. 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.

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

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

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

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

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

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

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

3. Originally Posted by masters
Hi bubblygirl,

You probably made a simple error somewhere.

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

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

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

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

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

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

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

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