# completing the square

• June 26th 2011, 07:40 AM
Khevish
completing the square
Complete the square:
2x^2+8x+1
• June 26th 2011, 08:00 AM
skeeter
Re: completing the square
Quote:

Originally Posted by Khevish
Complete the square:
2x^2+8x+1

$2x^2 + 8x + 1$

$2(x^2 + 4x) + 1$

$2(x^2 + 4x + 4) + 1 - 8$

finish it ...
• June 26th 2011, 08:23 AM
Khevish
Re: completing the square
how do you get -8? ^^
• June 26th 2011, 08:49 AM
Prove It
Re: completing the square
Maybe it would help if it was written like this

\displaystyle \begin{align*} 2(x^2 + 4x) + 1 &= 2(x^2 + 4x + 2^2 - 2^2) + 1 \\ &= 2(x^2 + 4x + 4 - 4) + 1 \\ &= 2(x^2 + 4x + 4) + 2(-4) + 1 \\ &= 2(x^2 + 4x + 4) - 8 + 1 \end{align*}