Find zeros of a polynomial function

Learn how to find zeros of a polynomial function with a few well-chosen examples.

Example #1

Find the zeros of f(x) = (x - 4)(x + 2)(x + 5)

Using the zero product property, find a zero for each linear factor

x - 4 = 0

x - 4 + 4 = 0 + 4

x = 4

x + 2 = 0

x + 2 - 2 = 0 - 2

x = -2

x + 5 = 0

x + 5 - 5 = 0 - 5

x = -5

The zeros of the function f(x) = (x - 4)(x + 2)(x + 5) are 4, -2, and -5

Example #2

Find the zeros of f(x) = x4 - x2

We cannot use the zero product property yet since we cannot see the linear factors.

Rewrite the function f(x) = x4 - x2 to show its linear factors. We can do this by factoring the function completely.

f(x) = x4 - x2

f(x) = x2(x2 - 1)

f(x) = (x)(x)(x - 1)(x + 1)

Now you can use the zero product property to find the zero for each linear factor.

x = 0

x = 0

x - 1 = 0

x - 1 + 1 = 0 + 1

x = 1

x + 1 = 0

x + 1 - 1 = 0 - 1

x = -1

The zeros of the function f(x) = x4 - xare 0, 1, and -1

Example #3

Find the zeros of f(x) = 8x3 - 8x2 - 160x

We cannot use the zero product property yet since we cannot see the linear factors.

Rewrite the function f(x) = 8x3 - 8x2 - 160x to show its linear factors. We can do this by factoring the function completely.

f(x) = 8x3 - 8x2 - 160x

f(x) = 8x(x2 - x - 20)

f(x) = 8x(x - 5)(x + 4)

Using the zero product property, find a zero for each linear factor

8x = 0

x = 0

x - 5 = 0

x - 5 + 5 = 0 + 5

x = 5

x + 4 = 0

x + 4 - 4 = 0 - 4

x = -4

The zeros of the function f(x) = 8x3 - 8x2 - 160x are 0, 5, and -4

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