# Need help with a "completing the square" problem in quadratic factoring!

• Aug 13th 2012, 11:34 AM
EJdive43
Need help with a "completing the square" problem in quadratic factoring!
When I try to solve x2+3x-10 just by factoring it from it's standard form I get x=-5 and x=2 which is good. But when I try to check that by using the "completing the square method" when you add (b/2)2 to both sides I get x=5/6 which is completely different as you can see. It is said that the "completing the square method works for any problem.
• Aug 13th 2012, 11:46 AM
HallsofIvy
Re: Need help with a "completing the square" problem in quadratic factoring!
Add $\displaystyle (b/2)^2$ to both sides of what? So far you don't have an equation. Please show exactly what you did. When I use "complete the square", I get the correct answer.
• Aug 13th 2012, 11:48 AM
Bean
Re: Need help with a "completing the square" problem in quadratic factoring!
$\displaystyle x^2+3x-10=0$

$\displaystyle x^2+3x=10$

$\displaystyle x^2+3x+\frac{9}{4}=10+\frac{9}{4}$

$\displaystyle (x+\frac{3}{2})^2=\frac{49}{4}$

$\displaystyle x+\frac{3}{2}=\frac{7}{2}, \frac{-7}{2}$

$\displaystyle x=2, -5$
• Aug 13th 2012, 11:50 AM
EJdive43
Re: Need help with a "completing the square" problem in quadratic factoring!
Thanks bean I forgot to square the 4