Question

Given the quadratic equation: f(x) = x2+4x-21

Answer 1

Answer:

x = - 7, x = 3

Step-by-step explanation:

To find the x- intercepts let f(x) = 0 , that is

x² + 4x - 21 = 0

Consider the factors of - 21 which sum to give the coefficient of the x- term (+ 4)

The factors are + 7 and - 3, since

7 × - 3 = - 21 and 7 - 3 = + 4, then

x² + 4x - 21 = 0

(x + 7)(x - 3) = 0 ← in factored form

Equate each factor to zero and solve for x

x + 7 = 0 ⇒ x = - 7

x - 3 = 0 ⇒ x = 3