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Some trinomials are prime. The only way to be certain a trinomial is prime is to list all the possibilities and show that none of them work.
Factor: .
Factors of 15 | Sum of factors |
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As shown in the table, none of the factors add to ; therefore, the expression is prime.
Factor: .
As shown in the table, you can use as the last terms of the binomials.
Factors of | Sum of factors |
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|
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Check.
Let’s summarize the method we just developed to factor trinomials of the form .
When we factor a trinomial, we look at the signs of its terms first to determine the signs of the binomial factors.
When c is positive, m and n have the same sign.
When c is negative, m and n have opposite signs.
Notice that, in the case when m and n have opposite signs, the sign of the one with the larger absolute value matches the sign of b .
Sometimes you’ll need to factor trinomials of the form with two variables, such as The first term, , is the product of the first terms of the binomial factors, . The in the last term means that the second terms of the binomial factors must each contain y . To get the coefficients b and c , you use the same process summarized in the previous objective.
Factor: .
Find the numbers that multiply to 36 and add to 12.
Factors of | Sum of factors |
---|---|
1, 36 | |
2, 18 | |
3, 12 | |
4, 9 | |
6, 6 |
Factor: .
We need in the first term of each binomial and in the second term. The last term of the trinomial is negative, so the factors must have opposite signs.
Find the numbers that multiply to and add to .
Factors of | Sum of factors |
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Factor: .
We need u in the first term of each binomial and in the second term. The last term of the trinomial is negative, so the factors must have opposite signs.
Find the numbers that multiply to and add to .
Factors of | Sum of factors |
---|---|
Note there are no factor pairs that give us as a sum. The trinomial is prime.
Factor Trinomials of the Form
In the following exercises, factor each trinomial of the form .
Factor Trinomials of the Form
In the following exercises, factor each trinomial of the form .
Mixed Practice
In the following exercises, factor each expression.
Consecutive integers Deirdre is thinking of two consecutive integers whose product is 56. The trinomial describes how these numbers are related. Factor the trinomial.
Consecutive integers Deshawn is thinking of two consecutive integers whose product is 182. The trinomial describes how these numbers are related. Factor the trinomial.
Many trinomials of the form factor into the product of two binomials . Explain how you find the values of m and n .
Answers may vary
How do you determine whether to use plus or minus signs in the binomial factors of a trinomial of the form where and may be positive or negative numbers?
Will factored as . Bill factored it as . Phil factored it as . Who is correct? Explain why the other two are wrong.
Answers may vary
Look at [link] , where we factored . We made a table listing all pairs of factors of 60 and their sums. Do you find this kind of table helpful? Why or why not?
ⓐ After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.
ⓑ After reviewing this checklist, what will you do to become confident for all goals?
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