How do you complete the square 4x^2-12x+3?

  • 0 votes

I'm doing Higher Maths, and until now i've always been fine with completing the square. I'm not sure why but i've completely lost my understanding of how to do it. I've been given the question 4x^2-12x+3 to complete, but I can't work out how to do it.. Could anyone give me really simple (i'm losing the will to live) steps to completing it?

I was given some instructions with this link http://www.bbc.co.uk/scotland/learning/bitesize/higher/maths/algebra/functions2_rev4.shtml (It's the last question) but it makes NO sense to me :( Please help!

Posted Sun 11th March, 2012 @ 10:32 by HannahBanana

2 Answers

  • 1 vote

1) ignore the +3 bit and just deal with the 4x^2-12x bit. This can be rewritten as (2x-3)^2 =0

2) This gives you 4x^2-12x+9. Now you must find the diffrence between this equation and the orginal equation. so you have to do (4x^2-12x+3) - (4x^2-12x+9). This equals -6.

3) put minus six on the end of your rewritten equation so it looks like this (2x-3)^2 -6=0

4) move the 6 over to the other side so (2x-3)^2 = 6

5) square root the six to get rid of the brackets so 2x-3 = +or- sqrt(6)

6) add three to both sides so 2x = +or- sqrt(6)+3

7) then divide the whole thing by 2 so x = (+or- sqrt(6)+3)/2

8) therefore the answer is x = 2.72 or 0.28 ( both to 2 d.p)

Answered Sun 11th March, 2012 @ 11:08 by Ewan
  • 0 votes

Thank you, I think I get that! :D

Answered Sun 11th March, 2012 @ 13:10 by HannahBanana