Question

What are the vertex and x-intercepts of the graph of y=x^2-4x-21?

Answer 1

Intercepts at (0,7) and (0,03)

Vertex at (2,-25)

Explanation:

Axis of symmetry is -b/2a = -(-4)/2(1) = 4/2 = 2 x=2

Plug x=2 into the equation and get 2^2-4(2)-21 = 4-8-21 = -25

Vertex is (2,-25)

Factor the equation (x-7)(x+3)

Set x-7=0, x=7

set x+3=0, x= -3

x intercepts at 7 and -3