Question

9. Find the vertex of f(x) = –2x2 - 4x – 8

a. Vertex: (-1,-6) b. Vertex: (-6,-1) C. Vertex: (2,1)
d. Vertex: (1,6)
e. Vertex: (1,-6)

Answer 1

A is the answer, (-1,-6) is the vertex.

Explanation:

With any quadratic, the formula for the x coordinate of the vertex is -b/2a.

In this case it is -(-4) / 2(-2) = 4 / -4 = -1.

To find the y, simply substitute the x.

f(-1) = -2(-1)² – 4(-1) – 8 = -2 + 4 – 8 = 2 – 8 = -6