SOLUTION: I am trying to learn, with great difficulty, how to factor this type of problem... 2a^2-2ab-24b^2 ... I have tried factoring out the 2, but I don't know how to go any further with

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: I am trying to learn, with great difficulty, how to factor this type of problem... 2a^2-2ab-24b^2 ... I have tried factoring out the 2, but I don't know how to go any further with       Log On


   



Question 7131: I am trying to learn, with great difficulty, how to factor this type of problem... 2a^2-2ab-24b^2 ... I have tried factoring out the 2, but I don't know how to go any further with this problem. How do I find the factors of 12 if there is no factor for the prceding term? Thank you so much for your help.
Found 2 solutions by Earlsdon, glabow:
Answer by Earlsdon(6294) About Me  (Show Source):
You can put this solution on YOUR website!
Well, you could start by factoring a 2 from the expression, just to simplify it a bit.
2a%5E2+-+2ab+-+24b%5E2 = 2%28a%5E2+-+ab+-+12b%5E2%29
Now let's look at the expression in the parentheses: a%5E2+-+ab+-+12b%5E2
The factors of the first term , a%5E2 would be %28a%29%28a%29
Look at the last term: -12b%5E2 and ask what are the factors of this term?
-12b%5E2 = %283b%29%28-4b%29 or %28-3b%29%284b%29 just to name a couple.
So, now try: %28a+%2B+3b%29%28a+-+4b%29 Using the FOIL method, multiply these factors:
%28a+%2B+3b%29%28a+-+4b%29+=+%28a%5E2+-+4ab+%2B+3ab+-+12b%5E2%29 Simplify to get:
a%5E2+-+ab+-+12b%5E2 and if you multiply by the 2 we factored at the start, we'll get:
2a%5E2+-+2ab+-+24b%5E2
So, the factors are: 2%28a%2B3b%29%28a-4b%29

Answer by glabow(165) About Me  (Show Source):
You can put this solution on YOUR website!
This is one of those things that have two approaches. One is art and the other is science. In this case, the art way is easier.
The polynomial
2a%5E2+-+2ab-24b%5E2%29 has an obvious factor, 2.
2%28a%5E2+-ab+-+12b%5E2%29 must be factored into binomials where
the a%5E2 term comes from a times a
the -12b%5E2 term comes from mb times nb, where m times n = -12
the -ab term comes from a times mb plus a time nb, where m plus n = -1
The numbers -4 and 3 satisfy the requirements: -4 times 3 = -12, and -4 plus 3 = -1.
So the factors are %28a+-4b%29+%28a+%2B+3b%29+=+a%5E2+-ab+-12b%5E2
The orginal polynomial is 2+%28a-4b%29%28a%2B3b%29