Zeros of a Polynomial Function
An important consequence of the Factor Theorem is that finding the zeros of a
polynomial is really the same thing as factoring it into linear factors. In this section we
will study more methods that help us find the real zeros of a polynomial, and thereby
factor the polynomial.
Rational Zeros of Polynomials:
The next theorem gives a method to determine all possible candidates for rational zeros
of a polynomial function with integer coefficients.
Rational Zeros Theorem:
If the polynomial ( ) 1
1 1 ... n n P x ax a x ax a n n
− = + ++ − + 0 has integer
coefficients, then every rational zero of P is of the form
p
q
where p is a factor of the constant coefficient 0 a
and q is a factor of the leading coefficient n a
Example 1: List all possible rational zeros given by the Rational Zeros Theorem of
P(x) = 6x
4
+ 7x
3
- 4 (but don’t check to see which actually are zeros) .
Solution:
Step 1: First we find all possible values of p, which are all the factors
of . Thus, p can be ±1, ±2, or ±4. 0 a = 4
Step 2: Next we find all possible values of q, which are all the factors
of 6. Thus, q can be ±1, ±2, ±3, or ±6. n a =
Step 3: Now we find the possible values of p
q by making combinations
of the values we found in Step 1 and Step 2. Thus, p
q will be of
the form factors of 4
factors of 6 . The possible p
q are
12412412412
, , , , , , , , , , ,
11122233366
± ± ± ± ± ± ± ± ± ± ±±
4
6