How to Graph Trig Functions on the TI84 Plus
The TI84 Plus calculator has builtin features especially designed for graphing trigonometric functions. They produce graphs that look like graphs you see in textbooks, and when you trace these graphs, the xcoordinate of the tracing point is always given as a fractional multiple of π. To use these features when graphing trigonometric functions, follow these steps:

Put the calculator in Function and Radian mode.
Press [MODE]. In the fourth line, highlight Radian, and in the fifth line highlight Function. (To highlight an item in the Mode menu, use the arrow keys to place the cursor on the item, and then press [ENTER].)

Enter your trigonometric functions into the Y= editor.
See the first screen.

Press [ZOOM][7] to graph the function.
[ZOOM][7] invokes the ZTrig command that graphs the function in a viewing window in which
It also sets the tick marks on the xaxis to multiples of π/2. Compare the graphing windows of ZStandard ([ZOOM][6]) and ZTrig in the last two screens.
When you trace a function graphed in a ZTrig window, the xcoordinate of the trace cursor will be a multiple of π/24, although the xcoordinate displayed at the bottom of the screen will be a decimal approximation of this value.
If you want to graph trigonometric functions in Degree mode, press [ZOOM][7]. The ZTrig window automatically adjusts to account for the mode of your calculator. Isn’t that nice?