# Thread: completing the square

1. ## completing the square

Complete the square:
2x^2+8x+1

2. ## Re: completing the square

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 ...

3. ## Re: completing the square

how do you get -8? ^^

4. ## 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*}