Division and Factoring
To factor a polynomial means to write it as a product of two or more simpler polynomials.
If we divide two polynomials and get 0 remainder, then we can write
dividend = (divisor)(quotient)
and we have factored the dividend. The dividend factors as the divisor times the
quotient if and only if the remainder is 0. We can use division to help us discover
factors of polynomials. To use this idea, however, we must know a factor or a
possible factor to use as the divisor.
Example 1
Using synthetic division to determine factors
Is x - 1 a factor of 6x3 - 5x2 - 4x + 3?
Solution
We can use synthetic division to divide 6x3 - 5x2 - 4x
+ 3 by x - 1:
1 |
6 |
-5 |
-4 |
3 |
|
↓ |
6 |
1 |
-3 |
|
6 |
1 |
-3 |
0 |
Because the remainder is 0, x - 1 is a factor, and
6x3 - 5x2 - 4x + 3 = (x - 1)(6x2 + x
- 3).
Example 2
Using division to determine factors
Is a - b a factor of a3 - b3?
Solution
Divide a3 - b3 by a - b. Insert zeros for the missing a2b- and ab2-terms.
Because the remainder is 0, a - b is a factor, and
a3 - b3 = (a - b)(a2 + ab + b2).
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