I'm trying to do a homework assignment on my graphing calculator app for my ipad (Quick graph+).

(Edit by Willie: The images are originally posted here http://imgur.com/a/XRj4g I've included them below.)

Image 1

Image 2

Image 3

Image 4

The first image at the top right is what I am trying to make on my graphing calculator. Basically I have to limit the domain when graphing. Halfway down in the red box I highlighted is the ears that we have to graph by limiting f(x)=-2abs(2x-5)+6 to a domain of 1<=x<=4

At the bottom right of the first image you can see how they insert it into the graphing calculator they use. They put f(x)=(-2abs(2x-5)+6)((x<=1)(x<=4)) however looking at the second image in the album my graphing calculator disallows that. I emailed the app creators and they said to use the "if" button. (image 3)

However when I used "if" it didn't turn out properly like I expected (image 4). I was wondering how I could go about properly graphing this function so it will limit the domain properly.

If there is any confusion in what I'm trying to do leave a comment and I'll try to explain my self further.

  • $\begingroup$ I've inlined your images. Unfortunately you do not have enough reputation yet to "save" a post with in-lined images. Drop me a line (by writing @Willie in a followup comment) if you need help with that. $\endgroup$ – Willie Wong Sep 25 '12 at 8:48
  • $\begingroup$ @WillieWong Thanks so much! Do you have any idea on how I can fix this issue? $\endgroup$ – matt Sep 25 '12 at 19:03

You used the if operator incorrectly. The format is

if( condition, what to do if True, what to do if False) 

But you put another condition in the place of "what to do if false".

Here's an example: I want a function which is equal to $3x$ between $x=1$ and $x=4$, is equal to $x+8$ between $x=4$ and $x=5$, and is undefined otherwise. The code could be

if(x>5, ln(0), if(x>4, x+8, if(x>1, 3*x, ln(0) ) ) )

Here I'm using $\ln(0)$ with the hope that it will simply produce no output for the corresponding range, rather than halt the entire computation. Don't have the app (or iPad for that matter), so can't tell for sure.

  • $\begingroup$ Thanks LVL it worked great! I've got it all working now $\endgroup$ – matt Sep 26 '12 at 23:59

You need to set the function to "undefined" when it is not in your region. Do you see any way to do that?

  • $\begingroup$ No I don't see a way of doing this. Every key I see can be found in image 4 $\endgroup$ – matt Sep 24 '12 at 23:05
  1. Just use desmos which is more efficient and functional


  1. wtf are you doing the graphing calculator questions lol
  2. is a cat really worth this much time and investment

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