Question

What are the zeros of f(x) = x2 + x - 20?

Answer 1

The zeroes are {-5, 4}.

Explanation:

f(x) = x^2 + x - 20 = 0

To factor this function we need 2 numbers whose sum is + 1 ( x = 1x) and whose product is -20. They are 5 and - 4 so we have:

(x + 5)(x - 4) = 0

x + 5 = 0 gives x = -5

and x - 4 = 0 gives x = 4.

Answer 2

x = - 5, x = 4

Explanation:

Given

f(x) = x² + x - 20

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, hence

(x + 5)x - 4) = 0 ← in factored form

Equate each factor to zero and solve for x

x + 5 = 0 ⇒ x = - 5

x - 4 = 0 ⇒ x = 4