I have been learning how to factor trinomials and I am stuck..
2x^2+x-15 = (2x-5)(x+3)
3a^2-2a-5 = (3a-5)(a+1)
Fc^2+17c+14 = (fc+7)(c+2)
To factor these types of problems, is the only way real to just plug in factors and do a full test with foil?? I mean some of these could have 100 possible factor pairs.. do you have to plug them in and keep going until it works? Am I missing a shortcut?
Aug 4th 2008, 01:00 PM
when you start out learning factoring you normally do it the harder way.
but there's some logic with factoring.
given , if the a is greater than one, you can do what's called the AC method.
For you first multiply the a and c.
That's -30. Since the linear term has a coefficient of +1, you need to find two numbers that multiply to give you -30 and add up to 1.
That's 6 and -5.
So rewrite this as:
Notice how I keep the -5x near the -15 since they have a common term.
Pull out a greatest common factor between terms:
Factor by grouping:
I might've went too fast, but we'll explain something more detailed if you ask the question.