How to Find the Equation of a Line on the TI84 Plus
The Eqns/Coords tool in theGeoMaster MEAS menu on the TI84 Plus calculator can be used to find the equation of a line, the equation of a circle, or the coordinates of an already constructed point. It will not find the equation of a segment, ray, vector, or side of a polygon.
To find the equation of a line or a circle, or to find the coordinates of a point, follow these steps:

Press [GRAPH][ZOOM][7] to select the Eqns/Coords tool from the MEAS menu.

Use the arrow keys to move the cursor to the object whose equation or coordinates you want to find and press [ENTER].
The equation or coordinates appear at the location of the cursor.

Use the arrow keys to move the equation or coordinates to a better location and press [ENTER] to anchor that location. Press [ENTER] again or move the cursor.
The Eqns/Coords tool remains active until you deactivate it. So if you want to find the equation of other lines or circles, or the coordinates of other points, repeat Steps 2 and 3. When you are finished using the tool, deactivate it by pressing [CLEAR] or by selecting another menu item.