Find the zeros of the polynomial function. f (x) = x3 5x2 - 4x - 20

You can factor this by grouping.

(x³ + 5x²) - (4x + 20) = x² (x+5) - 4 (x+5)

= (x² - 4) (x + 5)

Using the factored form of the difference of squares, this is

= (x - 2) (x + 2) (x + 5)

Zeros are the values of x that make these factors be zero.

x ∈ {-5, - 2, 2}