# quadratic function/inequality, multi-step problem and I am stuck

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• Mar 24th 2009, 09:30 AM
GatorGirl
quadratic function/inequality, multi-step problem and I am stuck
Hi everyone, happy Tuesday!

I am taking algebra and I just don't get quadratics. I have a sheet of different quadratic questions I have been working on since yesterday, trying to figure it out before coming here, but I failed :(

I have a couple questions below, thank you in advance for your help :)

2. f(x)=2+5x-3x^2
a. determine if it goes up or down..... down I got that far :)
b. find the vertex, this is where I got stuck
c. find axis of symmetry
d. find x- and y- intercepts
e. sketch the graph y=f(x)
f. determine whether the function has a maximum value or a minimum value, then find this value (What, I am so lost!)
g. find the range of f.

ahh why are there so many questions for one function!

3.) I am stuck on this one because the fractions killed me, er
solve the quadratic inequality:

1/2x^2 - 3/4x + 7 <(or equal, didn't know how to add the bar under) 0
• Mar 24th 2009, 09:39 AM
stapel
Quote:

Originally Posted by GatorGirl
2. f(x)=2+5x-3x^2
a. determine if it goes up or down..... down I got that far :)

I don't know what this means...? Since the quadratic is negative, the parabola does open downward....

Quote:

Originally Posted by GatorGirl
b. find the vertex, this is where I got stuck

To find the vertex, either complete the square or else use the formula "h = -b/(2a)".

Quote:

Originally Posted by GatorGirl
c. find axis of symmetry

The axis of symmetry is the vertical line "x = h" through the vertex.

Quote:

Originally Posted by GatorGirl
d. find x- and y- intercepts

To find a given intercept, plug "0" in for the other variable, and solve. So plug "0" in for "x" and evaluate to find the y-intercept, and then plug "0" in for "y" and solve the quadratic equation to find the x-intercept(s).

Quote:

Originally Posted by GatorGirl
e. sketch the graph y=f(x)

Graph in the usual way: Pick x-values, plug them into the formula, find the corresponding y-values, and draw the dots. Repeat until you are confident of the shape of the curve, and then sketch.

Quote:

Originally Posted by GatorGirl
f. determine whether the function has a maximum value or a minimum value, then find this value (What, I am so lost!)

Look at the graph. Look at the vertex. Use what you've learned about the relationship between the vertex of a parabola and the max/min points of quadratics.

Quote:

Originally Posted by GatorGirl
g. find the range of f.

The range is the output values. So look at the graph and figure out what values y can achieve. For instance, can y equal 5? (Wink)

Quote:

Originally Posted by GatorGirl
3.) solve the quadratic inequality:

1/2x^2 - 3/4x + 7 <(or equal, didn't know how to add the bar under) 0

To learn how to answer this, study a lesson on solving quadratic inequalities.
• Mar 24th 2009, 05:28 PM
rtblue
well. This looks like a perfect opportunity to try out latix :D, excuse me if i make a mistake.

I will help you with number 2, how to find the axis of symmetry.

So.. The Equation is ( i think, someone correct me if i am wrong):

$-3x^2\oplus5x\oplus2$

The formula to find the axis of symmetry is $\frac{-b}{2a}$

The standard form of a quadratic equation is: ax^2+bx+c (by the way guys, when i tried to do this in LATEX, it said error...)

So, just look at your equation, and find the $-b$(b is 5, so -b is -5) then find the $a$ (the a is -3, -3 times 2 is -6) and plug them into the equation, and that will give you the axis of symmetry.

So, the axis of symmetry is: $\frac{-5}{-6}$ which simplifies to $\frac{5}{6}$