Answer:
all real numbers less than or equal to 4
Step-by-step explanation:
To obtain the range we require the value of the y- coordinate of the vertex.
Given
f(x) = - (x + 5)(x + 1) ← equate f(x) to zero to find the zeros, 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
The vertex lies on the axis of symmetry which is at the midpoint of the zeros
=
=
= - 3
Substitute x = - 3 into f(x) for y- coordinate of vertex
= - (- 3 + 5)(- 3 + 1) = - (2)(- 2) = 4
The vertex = (- 3, 4 )
and - (x + 5)(x + 1) = - (x² + 6x + 5) = - x² - 6x - 5
Since the coefficient of the x² term is - 1 < 0
then the vertex is a maximum ∩
Hence range is [ 4, - ∞ )
That is all real numbers less than or equal to 4