My Math Forum Curious about high school factoring

 Algebra Pre-Algebra and Basic Algebra Math Forum

August 2nd, 2017, 09:53 AM   #11
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Quote:
 Originally Posted by labasa For example something like 3x^2 + 19x + 6
As 3 has only 1 and 3 as (positive) factors,

3x$^2$ + 19x + 6 = (3x + a)(x + b)

Now find a and b so that a * b = 6 and 3b + a = 19 hold.

Last edited by greg1313; August 2nd, 2017 at 09:56 AM.

August 2nd, 2017, 10:12 AM   #12
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Quote:
 Originally Posted by labasa Just wondering what is the easiest method to factorise ax^2 +bx + c at high school level... many thanks
Personally, I trying factoring for a minute or so. If I don't see a factoring quickly, I use the method specified in my previous post.

$ax^2 + bx + c = a * \left ( x + \dfrac{b + d}{2a} \right ) \left ( x + \dfrac{b - d}{2a} \right), \text { where } d = \sqrt{b^2 - 4ac}.$

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