Question

What are the vertex and x-intercepts of the graph of y=x2 - 4x -21? Select one answer for the vertex and one for the x-intercepts

Answer 1

Start with the x intercepts.
You need to factor the original function.
y = x^2 - 4x - 21
y = (x - 7)*(x + 3) These are the correct factors.

The two roots are
x = 7
x = - 3

So the two points you want are (7,0) and (-3,0)
That makes the answer C <<<<========

The vertex is a little harder. You need to complete the square to get it. (I take it you don't know any calculus yet.
y = x^2 - 4x - 21
y = (x^2 - 4x + ... ) - 21
y = (x^2 - 4x + 4) - 21 - 4
y = (x - 2)^2 - 25

The vertex is (2,- 25)
The answer is B <<<<<<=======