1. ## Completing the square.

I tried to complete the square (I think thats what it's called) when I multiplied (-2)(15)=-30 and get the factors of -30 that add up to -12 but none of them work e.g (-15) and (2) add up to -13 instead of -12.

I have no clue how to get it into the form that they have in the choices. Can anyone help me out?

2. ## Re: Help with math problem

$-2x^2 - 12x + 15$

$-2(x^2 + 6x) + 15$

$-2(x^2 + 6x + 9) + 15 + 18$

$-2(x+3)^2 + 33$

3. ## Re: Help with math problem

Originally Posted by skeeter
$-2x^2 - 12x + 15$

$-2(x^2 + 6x) + 15$

$-2(x^2 + 6x + 9 - 9) + 15$

$-2(x^2 + 6x + 9) + 15 - (9)(-2)$

$-2(x^2 + 6x + 9) + 15 + 18$

$-2(x+3)^2 + 33$
Thank you. I didn't get what you did at first, then I realized the steps you did in your head automatically. And I didn't know that you could factor only part of an equation (i.e. the first two terms but not the 15)

4. ## Re: Help with math problem

Originally Posted by Fenixx09
Thank you. I didn't get what you did at first, then I realized the steps you did in your head automatically. And I didn't know that you could factor only part of an equation (i.e. the first two terms but not the 15)
Kudos to you for thinking ... it's a rare activity these days.