# Completing the Square - Math Help Needed!

Discussion in 'Community Discussion' started by psycoswimmer, Nov 8, 2009.

1. ### psycoswimmer macrumors 65816

Joined:
Sep 27, 2006
Location:
USA
#1
So, I've been trying to figure out this problem for a while and I can't figure out how to do it. The question states: "Solve 2x^2 - 12x + 4 = 0 by completing the square, expressing the result in simplest radical form." I'm not sure how to continue with completing the square with a leading coefficient... I tried pulling out a 2 but then got confused up to the point were I had (2)(x+3)^2=7.

Any help is greatly appreciated!

2. ### AngryApple macrumors 6502

Joined:
Dec 25, 2008
#2
I don't know if I did it right:

x = 3 + root 7

3. ### fireshot91 macrumors 601

Joined:
Jul 31, 2008
Location:
Northern VA
#3
My first bet would be to factor it, making it 2(x^2-6x+2)=0, but that leads you nowhere, since you can't factor that anymore.

4. ### sammich macrumors 601

Joined:
Sep 26, 2006
Location:
Sarcasmville.
#4
Your first step is to get the coeff of x^2 to be equal to 1

Stepwise:

.x² - 6x + 2 = 0............after dividing by 2
(x² - 6x + 9) + 2 . 9 = 0...complete the square: add (b/2)² = 9
(x - 3)² = 7................solving for x
.x - 3...= √7
.x.......= -3 - √7

5. ### imaketouchtheme macrumors 65816

Joined:
Dec 5, 2007
#5
Ok, when there's a coefficient in front of the x^2, you have to first divide the entire equation by the coefficient, which will look like this:

x^2-6x+2=0

All I did was divide everything by 2.

After that, move your "c" term over (since the equation is in the form of ax^2-bx+c=0)

Now you have x^2-6x=-2

If you need anymore help from there, let me know.

6. ### Tomorrow macrumors 604

Joined:
Mar 2, 2008
Location:
Always a day away
#6
Fixed. You were close. Remember, a quadratic equation can have two roots, often related to the positive and negative roots of (b^2-4ac). It's a good idea to check your work using the quadratic formula.

7. ### sammich macrumors 601

Joined:
Sep 26, 2006
Location:
Sarcasmville.
#7
Oh man, bad memories of little mistakes in maths exams.

Thanks for fixing those up for me. And to think, I'm studying engineering

8. ### Tomorrow macrumors 604

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Mar 2, 2008
Location:
Always a day away
#8
You poor soul. (spoken by a 40-year-old engineer)

9. ### psycoswimmer thread starter macrumors 65816

Joined:
Sep 27, 2006
Location:
USA
#9
Thanks everyone, I finally got it. And yes, the answer is 3 ± √7.