Answer:
x = - 4, x = 5
Explanation:
To find the zeros equate f(x) to zero, that is
x² - x - 20 = 0
Consider the factors of the constant term (- 20) which sum to give the coefficient of the x- term (- 1)
The factors are - 5 and + 4, since
- 5 × 4 = - 20 and - 5 + 4 = - 1, thus
(x - 5)(x + 4) = 0 ← in factored form
Equate each factor to zero and solve for x
x + 4 = 0 ⇒ x = - 4
x - 5 = 0 ⇒ x = 5