How do you know when to use the quadratic formula?

  • 1 vote

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Posted Wed 6th June, 2012 @ 20:05 by Ameenah:)

7 Answers

  • 6 votes

Usually a hint would be as the question would say, 'leave your answer to three significant figures' - in this case, the only practical and possible way is to use the quadratic formula. In other cases, factorise as you normally would but if you come to an equation that is almost impossible to factorise - use the quadratic formula :) Hope that helped.

Answered Wed 6th June, 2012 @ 21:16 by Terrie
  • 2 votes

Ameenah:) wrote:

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general form of a quadratic equation is ax^2+bx+c=0

you use the quadratic formula when b^2-4ac does not equal n^2 (a square number)

if b^2-4ac=n^2 (a square number) then you know that it can be factorised otherwise use the quadratic formula!

hope this helps.

Answered Wed 31st October, 2012 @ 21:17 by gaffer dean
Edited by gaffer dean on Fri 19th April, 2013 @ 19:58
  • 1 vote

We were told to use the quadriatic formula if you can't factorise (1st thing) and can't complete the square (2nd thing)

Answered Mon 10th December, 2012 @ 20:42 by KatieL
  • 0 votes

Take a look at these clips which explain the quadratic formula and exam question on them.

http://www.youtube.com/watch?v=aeA5L-4SrmQ&list=PLA389938897F32FD7&index=5&feature=plpp_video

http://www.youtube.com/watch?v=l7_4D6gzE2w&list=PLA389938897F32FD7&index=6&feature=plpp_video

Answered Wed 6th June, 2012 @ 23:17 by Mr Hegarty
  • 0 votes

Normally if it does not say specifically to use complete the square, and if it does not look simple enough to just do by itself, then I use the quadratic formula :)

Answered Sat 9th June, 2012 @ 15:27 by OneTooManyAnOpinion
  • 0 votes

I think it's when the answer says leave your answer to 3sf or when you can't factorise it. I'm rubbish at factorising so I use it all the time as it always works.

Answered Tue 19th June, 2012 @ 16:27 by Thegirlwhoknewtoomuch - Team GR
  • -2 votes

I think when there is unequal first difference, you need to find the second difference which leads into the quadratic formula. Not fully understand your question. An example would give a better response. 

Answered Wed 6th June, 2012 @ 20:09 by Shree