I have a TI-84 Plus and it will not graph two functions at once and I need it to do this for my Calculus homework.

amazing - all I did was search for ti84 studycrd and look what I found. The question is why couldn't you do it? Maybe you need to switch to a 4 fct unit.
TI-84 StudyCard app - techpoweredmath.com https://www.techpoweredmath.com/ti-84-studycard-ap/
TI-84 StudyCard app. The Texas Instruments website has a huge number of studycard stacks that cover every subject, not just math. You'll find every kind of math stack you could think of too. They include topics as varied as multiplication facts, graphs of common functions, to calculus definitions and trig identities.

Complete with zeros.

Is it somehow preventing you from graphing, or are you simply not getting the graph you expect?

Most likely you have the angular mode set wrong. You probably want it set to radians. Press MODE, move to the third line, highlight RADIAN, press ENTER, then 2ND [QUIT].

If it's not the angular mode, please reply to this post and give an example or two.

To clean the slate so to speak, just reset the RAM.

1. Press [2nd][+] to access the (MEM)ory management function
2. Press [7:Reset]
3. Press [1:All Ram]
4. Press [2:Reset]
5. Press [CLEAR] to erase the "RAM cleared" Message

Calc

If you have used or just run the Transfrm Application, you will no longer be able to draw more than one graph.
To restore the native OS graphing capabilities Uninstall the Transfrm Application. Here is how to do it.

1. Press the [APPS] key.
2. Scroll Up to reach the bottom of the list faster.
3. Point to Transfrm and press [ENTER].
4. Select [1:Uninstall]
   

Note: Do not worry about Uninstall, it will merely kick the application from memory. Transfrm will still remain in calculator.

In order to select additional graphs, the Transformation Graphing Application will need to be uninstalled from the TI-83 Plus Family and TI-84 Plus Family.

More information regarding this matter can be found in the Knowledge Base. The Knowledge Base can be accessed by clicking on the URL below:

http://epsstore.ti.com/OA_HTML/csksxvm.jsp?nSetId=65121&nUsePub=NO&jttst0=6_23871,23871,-1,0,&jtfm0=&etfm1=&jfn=ZG14E1108A3A0CD3ABADCD67260B59BDE0CEEA20790F80F708D8A4FDACCD82D31F792BC1B01D2F67ECAE6718104B82CC1C8F

Press the 2nd button, then the plus button, the 7, then 1, then 2. This will reset your calculator.

it is a function if it passes the verticle line test. That is if you graph a problem and a verticle line passes through the problem only once then it is a function. If the verticle line passes through the problem more than once it is not a function.

I think you should get a Texas Instruments calculator and push the 'y=' button then put the equation like '2x+4' in the y1 area. You can put the X by using the variable botton. I hope my english makes sense I am not a native speaker.

Put the calculator in radian mode and it will graph trig functions just fine. If you don't know how to change it to radians, then go to mode and cursor over to select radians. I am assuming you know where the sine, cosine, tangent, etc. keys are.