Learning Outcomes
- Use the distributive property to multiply two binomials
Just like there are different ways to represent multiplication of numbers, there are several methods that can be used to multiply a binomial times a binomial.
Using the Distributive Property
We will start by using the Distributive Property. Look again at the following example.
We distributed the [latex]p[/latex] to get | [latex]x\color{red}{p}+3\color{red}{p}[/latex] |
What if we have [latex]\left(x+7\right)[/latex] instead of [latex]p[/latex] ?
Think of the [latex]x+7[/latex] as the [latex]\color{red}{p}[/latex] above. |
|
Distribute [latex]\left(x+7\right)[/latex] . | |
Distribute again. | [latex]{x}^{2}+7x+3x+21[/latex] |
Combine like terms. | [latex]{x}^{2}+10x+21[/latex] |
Notice that before combining like terms, we had four terms. We multiplied the two terms of the first binomial by the two terms of the second binomial—four multiplications.
Be careful to distinguish between a sum and a product.
[latex]\begin{array}{cccc}\hfill \mathbf{\text{Sum}}\hfill & & & \hfill \mathbf{\text{Product}}\hfill \\ \hfill x+x\hfill & & & \hfill x\cdot x\hfill \\ \hfill 2x\hfill & & & \hfill {x}^{2}\hfill \\ \hfill \text{combine like terms}\hfill & & & \hfill \text{add exponents of like bases}\hfill \end{array}[/latex]
example
Multiply: [latex]\left(x+6\right)\left(x+8\right)[/latex]
Solution
[latex]\left(x+6\right)\left(x+8\right)[/latex] | |
Distribute [latex]\left(x+8\right)[/latex] . | [latex]x\color{red}{(x+8)}+6\color{red}{(x+8)}[/latex] |
Distribute again. | [latex]{x}^{2}+8x+6x+48[/latex] |
Simplify. | [latex]{x}^{2}+14x+48[/latex] |
try it
Now we’ll see how to multiply binomials where the variable has a coefficient.
example
Multiply: [latex]\left(2x+9\right)\left(3x+4\right)[/latex]
try it
In the previous examples, the binomials were sums. When there are differences, we pay special attention to make sure the signs of the product are correct.
example
Multiply: [latex]\left(4y+3\right)\left(6y - 5\right)[/latex]
try it
Up to this point, the product of two binomials has been a trinomial. This is not always the case.
example
Multiply: [latex]\left(x+2\right)\left(x-y\right)[/latex]
try it
To see another example of how to visualize multiplying two binomials, watch the following video. We use an area model as well as repeated distribution to multiply two binomials.
Candela Citations
- Question ID 146210, 146209, 146208, 146207. Authored by: Lumen Learning. License: CC BY: Attribution
- Multiply Binomials Using An Area Model and Using Repeated Distribution. Authored by: James Sousa (mathispower4u.com). Located at: https://youtu.be/u4Hgl0BrUlo. License: CC BY: Attribution
- Prealgebra. Provided by: OpenStax. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/contents/caa57dab-41c7-455e-bd6f-f443cda5519c@9.757