# Thread: Graphing a function in the window?

1. ## 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.

2. 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.

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.

3. 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.

4. 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.

5. 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?

6. 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).

7. screenshots ...

8. 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.

9. 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.
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 ...

Graph

11. I just tried graphing it on a graphing calculator and it gave me this:

12. Originally Posted by krzyrice
I just tried graphing it on a graphing calculator and it gave me this:
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?

13. Originally Posted by krzyrice
I just tried graphing it on a graphing calculator and it gave me this:
that is not the function the exercise gave you ... $\displaystyle y = -x\left(\frac{x-1000}{900}\right)$

looks like you graphed $\displaystyle y = x^2$

14. 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.

15. 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 $\displaystyle -10\le x\le 10$, $\displaystyle -10\le y\le -10$

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

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