# Graphing a function in the window?

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• Jan 30th 2010, 05:14 PM
krzyrice
Graphing a function in the window?
I need help with this problem. So do I start out with plugging in random values for x? Such as -2, -1, 0, 1, 2 and so on. And what do they mean by the "Graph the following function in the window -10 < x < 10, -10 < y < 10?" Thank you.

http://i50.tinypic.com/8yuzb7.jpg
• Jan 30th 2010, 05:19 PM
Prove It
Quote:

Originally Posted by krzyrice
I need help with this problem. So do I start out with plugging in random values for x? Such as -2, -1, 0, 1, 2 and so on. And what do they mean by the "Graph the following function in the window -10 < x < 10, -10 < y < 10?" Thank you.

http://i50.tinypic.com/8yuzb7.jpg

Expand it out, so that you have

$\displaystyle y = -\frac{1}{900}x^2 + \frac{10}{9}x$.

You should know how to graph quadratics by finding $\displaystyle x$ and $\displaystyle y$ intercepts and turning points.
• Jan 30th 2010, 05:25 PM
krzyrice
So like I said do I just plug in random values of x now and find the y values of it? Then I graph the equation and find the average rate of change to see if it is a line or not? Thanks for helping me so far.
• Jan 30th 2010, 05:50 PM
Prove It
Is a Quadratic function ever a line?

Like I said, the easiest way to sketch a graph is to find the $\displaystyle x$ and $\displaystyle y$ intercepts and the turning point. This gives you an idea of the shape of the graph.

And then yes, you can plot points to make your graph a bit more accurate.
• Jan 30th 2010, 05:57 PM
krzyrice
Nope a quadratic it's never a line. But What I don't get is what is the -10 < x < 10 and -10 < y < 10 for? What am I suppose to do with those?
• Jan 30th 2010, 06:09 PM
mr fantastic
Quote:

Originally Posted by krzyrice
Nope a quadratic it's never a line. But What I don't get is what is the -10 < x < 10 and -10 < y < 10 for? What am I suppose to do with those?

You are being told what scale to use on your x and y-axes (potentially, you're meant to graph this on a Graphing calculator and you're being told what window to use).
• Jan 30th 2010, 06:36 PM
skeeter
screenshots ...
• Jan 30th 2010, 07:27 PM
krzyrice
I thought the shape was suppose to be a parabola. Dang this problem is giving me a hard time. Sorry I don't have a graphing calculator so I don't really know how to solve this. And my teacher makes us write out the answer and explain how we got it also. (Worried)
• Jan 30th 2010, 07:46 PM
skeeter
Quote:

Originally Posted by krzyrice
I thought the shape was suppose to be a parabola. Dang this problem is giving me a hard time. Sorry I don't have a calculator so I don't really know how to solve this. And my teacher makes us write out the answer and explain how we got it also. (Worried)

the graph is a parabola ... you're only looking at a very small section of the graph in the given window.

here's how it looks in an expanded window ...
• Jan 30th 2010, 07:48 PM
skeeter

Graph
• Jan 30th 2010, 08:59 PM
krzyrice
I just tried graphing it on a graphing calculator and it gave me this:
http://i45.tinypic.com/mcsz0n.jpg
• Jan 31st 2010, 02:34 AM
HallsofIvy
Quote:

Originally Posted by krzyrice
I just tried graphing it on a graphing calculator and it gave me this:
http://i45.tinypic.com/mcsz0n.jpg

Okay, what window did you use? What does the graph look like if you set the window to $\displaystyle -10\le x\le 10$, $\displaystyle -10\le y\le -10$ as in your problem?
• Jan 31st 2010, 04:48 AM
skeeter
Quote:

Originally Posted by krzyrice
I just tried graphing it on a graphing calculator and it gave me this:
http://i45.tinypic.com/mcsz0n.jpg

that is not the function the exercise gave you ... $\displaystyle y = -x\left(\frac{x-1000}{900}\right)$

looks like you graphed $\displaystyle y = x^2$
• Jan 31st 2010, 10:41 AM
krzyrice
In the calculator I typed in -x(x-1000/900). Should I have typed it differently? I also tried your way -x(x-1000)/900 and got a straight line. And even if I select zoomfit it would still show a straight line.

http://i45.tinypic.com/wvvdqu.jpg
• Jan 31st 2010, 10:45 AM
krzyrice
Quote:

Originally Posted by HallsofIvy
Okay, what window did you use? What does the graph look like if you set the window to $\displaystyle -10\le x\le 10$, $\displaystyle -10\le y\le -10$ as in your problem?

This is what it looks like when I use $\displaystyle -10\le x\le 10$, $\displaystyle -10\le y\le -10$

http://i48.tinypic.com/ipuqsm.jpg

Also I input the equation in the calculator as -x((x-1000/900))
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