Lesson Plan - Get It!
Kristen: What is u times r times r?
Kristen: No, I'm not!
When you multiply polynomials (an expression that has more than one term), you have to pay close attention to what you are multiplying.
In this lesson, you will learn how to multiply two sets of monomials together, and how to multiply a polynomial by a monomial. If you have not completed the previous lessons in this Polynomials series, please go to Related Lessons in the right-hand sidebar.
To multiply monomials (an expression with only one term, such as 3y2) and polynomials by monomials, you need to use exponent rules. If you are not comfortable with exponents, please watch Exponent Rules Song – Learn Algebra – Learning Upgrade as a review:
Multiplying monomials is similar to multiplying two numbers together, but with a few added steps:
- When you multiply variables, you must first identify the coefficients (plain old numbers), and group them together.
- Next, group like variables.
- Finally, multiply all like sets.
Remember, a variable without an exponent carries an implied exponent of 1, so be sure to include the 1 when multiplying (which, in the case of exponents, is technically adding) like terms.
Let's try some examples:
- Identify like terms (coefficients and x's:) (5x2)(4x3)
- Rearrange into coefficients and variables, in this case, x's: (5 * 4)(x2 - x3)
- Multiply the terms to get your answer: 20x5
Example with two different variables: (-3x3y2)(4xy5)
- Identify like terms (coefficients, x's, and y's): (-3x3y2)(4xy5)
- Rearrange: (-3 * 4)(x3 * x)(y2 * y5)
- Multiply terms to get answer: -12x4y7
Try your hand at multiplying monomials and share your results with a parent or teacher. Drag the correct answer into the answer space:
To multiply a polynomial by a monomial, use the distributive property and multiply each term inside the parenthesis by the term outside the parenthesis.
Before we begin, let's review the Distributive Property. It is the property of multiplication that states that multiplying a sum by a number is the same as multiplying each addend by the number, then adding the products. The Distributive Property says that if a, b, and c are real numbers, then: a x (b + c) = (a x b) + (a x c). If you still don't get it, here's a wacky video all about the Distributive Property of Multiplication that should clear things up nicely.
Once you're ready, and feel comfortable with the Distributive Property, take a look at these examples:
Example 1: 2(3a2 + 8a +11)
Distribute the outside monomial (2) to each term inside the parenthesis.
- (2)3a2+ (2)8a + (2)11 — All like terms are together.
- 6a2+ 16a + 22 — Multiply to get your final answer.
Example 2: 2x2y(3x-y)
- 2x2y(3x) - 2x2y(y) — Distribute the outside monomial to each term inside the parenthesis.
- (2 * 3)(x * x2)(y) - (2)(x2)(y * y)
Group like terms together.
- 6x3y - 2x2y2 — Multiply to get your final answer.
Example 3: 4a(a2b+2b2)
- 4a(a2b) + 4a(2b2) — Distribute the outside monomial to each term inside the parenthesis.
- (4)(a * a2)(b) + (4 * 2)(a)(b2) — Group like bases together.
- 4a3b + 8ab2 — Multiply together to get your final answer.
Try the next few practice problems and share your answer with a parent or teacher. Drag the correct answer into the answer space:
Now that you have an understanding of how to multiply monomials — and polynomials by monomials —by grouping like bases, let's practice.