This module is from Elementary Algebra by Denny Burzynski and Wade Ellis, Jr.
Factoring is an essential skill for success in algebra and higher level mathematics courses. Therefore, we have taken great care in developing the student's understanding of the factorization process. The technique is consistently illustrated by displaying an empty set of parentheses and describing the thought process used to discover the terms that are to be placed inside the parentheses.The factoring scheme for special products is presented with both verbal and symbolic descriptions, since not all students can interpret symbolic descriptions alone. Two techniques, the standard "trial and error" method, and the "collect and discard" method (a method similar to the "ac" method), are presented for factoring trinomials with leading coefficients different from 1.
Objectives of this module: know how to factor a polynomial using the grouping method and when to try the grouping method.
Overview
- Using Grouping to Factor a Polynomial
- Knowing when to Try the Grouping Method
Using grouping to factor a polynomial
Sometimes a polynomial will not have a particular factor common to every term. However, we may still be able to produce a factored form for the polynomial.
The polynomial
has no single factor that is common to every term. However, we notice that if we
group together the first two terms and the second two terms, we see that each resulting binomial has a particular factor common to both terms.
Factor
out of the first two terms, and factor
out of the second two terms.
Now look closely at this binomial. Each of the two terms contains the factor
.
Factor out
.
is the final factorization.
Knowing when to try the grouping method
We are alerted to the idea of grouping when the polynomial we are considering has
either of these qualities:
- no factor common to
all terms
- an
even number of terms
When factoring by grouping, the sign
of the factor we are taking out will
usually (but not always) be the same as the sign of the first term in that group.
Sample set a
Factor
.
- We notice there is no factor common to all terms.
- We see there are four terms, an even number.
- We see that terms 1 and 2 have
in common (since the 1st term in the group is
.
- We notice that the 3rd and 4th terms have
in common (since the 1st term in the group is
).
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Practice set a
Use the grouping method to factor the following polynomials.
When factoring the polynomial
in Sample Set A, we grouped together terms1 and 2 and 3 and 4. Could we have grouped together terms1 and 3 and 2 and 4? Try this.
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Do we get the same result? If the results do not look precisely the same, recall the commutative property of multiplication.
Exercises
For the following problems, use the grouping method to factor the polynomials. Some polynomials may not be factorable using the grouping method.
Exercises for review