Calculate the zeros of the function y=-X^2-4x+21

x = - 7, x = 3

Step-by-step explanation:

To find the zeros let y = 0, that is

- x² - 4x + 21 = 0 (multiply through by - 1)

x² + 4x - 21 = 0

Consider the factors of the constant term ( - 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, thus

(x + 7) (x - 3) = 0

Equate each factor to zero and solve for x

x + 7 = 0 ⇒ x = - 7

x - 3 = 0 ⇒ x = 3