Multiplying Polynomials
Multiplying Polynomials with Two or More Terms
We can use the Distributive Property to multiply two polynomials where at
least one of the polynomials has two or more terms.
For example, suppose we wish to find the product (a + b)(c + d + e).
Distribute (c + d + e) to
both a and b. |
(a + b)(c + d + e) |
= a(c + d + e) + b(c + d + e) |
Distribute both a and b to
each term in (c + d + e). |
|
= ac + ad + ae + bc + bd + be |
Notice that each term in the first polynomial is multiplied by each term in
the second polynomial. That is, a is multiplied by c, d, and e. Also, b is
multiplied by c, d, and e.
This suggests a general procedure for multiplying any two polynomials.
Procedure — Multiplying Polynomials with Two or More Terms
Step 1 Multiply each term in the first polynomial by each term in
the second polynomial.
Step 2 Simplify.
Example
Find: (3x - 4)(x3 - 5x + 8)
Solution
Step 1 Multiply each term in the first polynomial by each term in the
second polynomial.
Multiply 3x by x3, -5x, and 8. Then multiply -4 by x3,
-5x, and 8.
(3x - 4)(x3 - 5x +
8) |
= = |
(3x)(x3) 3x4
|
+ - |
(3x)(-5x) 15x2 |
+ + |
(3x)(8) 24x |
+ - |
(-4)(x3) 4x3 |
+ + |
(-4)(-5x) 20x |
+ - |
(-4)(8) 32 |
Step 2 Simplify
Combine like terms and
write the terms in
descending order. |
= 3x4 - 15x2 + 24x - 4x3
+ 20x - 32 |
So, (3x - 4)(x3 - 5x + 8) = 3x4 - 15x2 + 24x
- 4x3 + 20x - 32.
|