problem! quadratic function / max. value

[Guest]

How in the world do I answer this problem??

Which of the following is a quadratic function that has a maximum value of 2 when x = –1 and one x-intercept is –3?

A. f (x) = x^2 – 6x – 5
B. f (x) = –x^2 – x + 6
C.

D. f (x) = 2x^2 – x – 15

I don't even know how to begin it!

 

[pka]

In order for a quadric function to have a maximum, its graph opens down. That happens in just two of the given functions. You also know that f(-3)=0 & f(-1)=2.

 

[skeeter]

the vertex of a parabola w/ equation f(x) = ax² + bx + c is located at
x = -b/(2a), and has a max or min value (depending on the sign of a) at f(-b/(2a)).