Find a Pair of Factors of AC Whose Sum is BDate: 04/12/2002 at 00:08:38 From: Robert Draper Subject: A C bust B? factoring When I was a freshman, I was taught a method called either A B Bust C or A C Bust B. Over the years, my memory of this method has faded and I do not remember exactly how to do it. Do you have any knowledge of this method? Thank you. Robert Date: 04/12/2002 at 12:05:49 From: Doctor Peterson Subject: Re: A C bust B? factoring Hi, Robert. I wonder if the "AC method" discussed here might be what you have in mind: A C Method - Student Learning Assistance Center, Southwest Texas State University http://www.swt.edu/slac/math/ACMethod.html Factoring Trinomials - Dr. Math archives http://mathforum.org/library/drmath/view/56442.html The idea (which is worded a little oddly in the first, and hidden in the middle of the second) is to find a pair of factors of AC whose sum is B. For example, to factor 6x^2 + 25x - 9, AC = 54 = -2*3*3*3, and if we choose AC = -2*27, the sum of the factors is 25. Then we write it as 6x^2 + 27x - 2x - 9 and factor by grouping: 3x(2x + 9) - (2x + 9) (3x - 1)(2x + 9) I agree that this is a lot easier than the method I learned. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994- The Math Forum at NCTM. All rights reserved.
http://mathforum.org/dr.math/