13.
In this case, there is a common factor that we can factor out.
The expression inside the parentheses is then one of the easier
factoring problems.
If we do not factor out the common factor first, the problem
can still be done. Multiply the first and last coefficients, and find a
pair that add up to the middle one.
The FOIL step, then, looks like
This will factor as
which looks a little different from out other answer. But if you notice,
both of the terms in the first binomial factor have a common factor
of 2 which can be factored out,
leaving us with the same factors we got when we did the problem
the other way.
If there is a common factor that can be factored out, one will
have a choice between whether to factor it out at the beginning or to
factor it out later. You will find that it will make your job easier if
you factor out the common factor at the beginning of the problem.