# Thread: Forms of Quadratic Functions HELP!

1. ## Forms of Quadratic Functions HELP!

Hi everyone!
Some of the problems below are answered but I need someone to check if I'm correct but some problems are also empty and those are the ones I am having trouble with. Please help! Thank you so much.

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f(x) = x^2-8x-9

a) Give f(x) in factored form.
Answer: f(x) = (x-9)(x+1)

b) Give f(x) in vertex form.
Answer: f(x) = (x-4)^2-25

c) Give the vertex of f(x) and its axis of symmetry.
Answer: Not sure how to get this!

d) Does f(x) have an absolute minimum OR an absolute maximum? What is its minimum or maximum value?
Answer: Not sure how to get this!

e) Give the interval on which f(x) is decreasing.
Answer: Not sure how to get this!

f) What are the zeros of f(x) ? (its x-intercepts)
Answer: x-intercepts => (9,0) and (-1,0)

g) What is the y-intercept of f(x) ?
Answer: y-intercept => (0,-9)

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Please help me on the red parts =\ THANK YOU!

2. Originally Posted by RedSpades
c) Give the vertex of f(x) and its axis of symmetry.
Answer: Not sure how to get this!
For a parabola,
$y=ax^2+bx+c,a\not = 0$.
The axis of symettry is always.
$-\frac{b}{2a}$.