Solution 10356: Solving Simultaneous Equations on the TI-85 or TI-86.
How do I solve simultaneous equations on the TI-85 or TI-86?
The example below will demonstrate how to use the SIMULT function to solve simultaneous equations on the TI-85 or TI-86.
Example: Solve the following for x, y and z.
3x + 3y - 4z = -3
-x + 2y + 5z = 18
8x + 4y - 7z = -5
1) Press [2nd] [SIMULT]
2) Input 3 (This indicates that there are three equations to solve.)
3) Press [ENTER]
4) Input the coefficients for the first equation pressing [ENTER] after each value.
5) Press  [ENTER]  [ENTER] [(-)]  [ENTER] [(-)]  [ENTER].
6) Repeat the same steps for the next two equations.
7) Press [F5] to display the results.
The given solution will show:
Please see the TI-85 and TI-86 guidebooks for additional information.