5.6 – Find the Rational Zeros

5.6 – Find the Rational Zeros

Example 1:

List the possible rational zeros of f using the rational zero theorem.

a. f(x) = x 3 + 2x 2 – 11x + 12 b. f(x) = 4x 4 – x 3 – 3x 2 + 9x - 10

5.6 – Find the Rational Zeros

Verifying Zeros

In Lesson 5.5, you found zeros of polynomial functions when one zero was known. The rational zero theorem is a starting point to find zeros when NO zeros are known.

However, the rational zero theorem lists only

possible

zeros. In order to find the

actual

zeros of a polynomial function f, you must test values from the list of possible zeros.

5.6 – Find the Rational Zeros

Example 2:

Find all real zeros of f(x) = x 3 – 8x 2 + 11x + 20

5.6 – Find the Rational Zeros

Example 2b:

Find all real zeros of f(x) = x 3 – 5x 2 + 7x – 35

5.6 – Find the Rational Zeros

Limiting the search for zeros

In the previous examples, the leading coefficient of the polynomial is 1. When the leading coefficient is not 1, the list of possible rational zeros can increase dramatically. In such cases, the search can be shortened by sketching the function’s graph.

5.6 – Find the Rational Zeros

Example 3:

Find all real zeros of f(x) = 10x 4 – 11x 3 – 42x 2 + 7x + 12