Question

The function f(x)=-(x+5)(x+1) is shown. What is the range of the function?​

Answer 1

(- ∞, 4 ]

Explanation:

To determine the range we require the coordinates of the vertex

The vertex lies on the axis of symmetry which is positioned at the midpoint of the zeros.

To obtain the zeros, equate f(x) to zero, that is

-(x + 5)(x + 1) = 0

Equate each factor to zero and solve for x

x + 5 = 0 ⇒ x = - 5

x + 1 = 0 ⇒ x = - 1

`x_(vertex)` =
`(-5-1)/(2)` =
`(-6)/(2)` = - 3

Substitute x = - 3 into f(x) for corresponding value of y

f(- 3) = - (- 3 + 5)(- 3 + 1) = - (2)(- 2) = 4

Vertex = (- 3, 4)

Since a = - 1 then vertex is a maximum, hence

range is (- ∞, 4 ]