How to Solve a System of Equations on the TI-84 Evo

The TI-84 Evo has a System Solver app built in that works out a whole system of equations on its own.

Open the System Solver

  1. Press on for the app grid, and arrow onto the two-stacked-equations icon. The bar along the top reads SYSTEM SOLVER when you have the right one. If the icon is missing, restoring your missing apps brings it back.
    The TI-84 Evo app grid with the System Solver icon highlighted and SYSTEM SOLVER named in the title bar
  2. Press enter. The SETUP screen comes up. Leave EQUATIONS and UNKNOWNS on 2 for a two-equation system.
    The TI-84 Evo System Solver SETUP screen with EQUATIONS and UNKNOWNS both set to 2 and variables x, y
  3. Press NEXT. The five labels along the bottom of the screen belong to the top-row f1 to f5 keys. NEXT sits above graph.
    The TI-84 Evo top row of keys with the graph key highlighted
    The TI-84 Evo System Solver entry grid, two blank rows reading 0x plus 0y equals 0

Enter the system and solve

This walk-through solves 2x + 3y = 12 and x − y = 1.

  1. Type the first coefficient. Press 2. Digits land on the entry line at the bottom of the screen. Press enter and the 2 drops into the box, and the highlight jumps to the sign.
    The TI-84 Evo System Solver with 2 entered as the first coefficient and the plus sign highlighted, prompting Press plus or minus
  2. Set the sign to plus. The signs between the terms are their own boxes, and the prompt at the bottom says Press [+] or [-]. Press +, then enter.
  3. Finish the first equation. Press 3, enter for the y, then 1, 2, enter for the 12. The top line now reads 2x + 3y = 12.
  4. Start the second equation. Press 1, enter for its x. This sign is a minus, so press the − subtraction key, not the (-) negative key (which does nothing here), then enter.
  5. Finish the second equation. Press 1, enter for the y, then 1, enter for the 1 on the right.
    The TI-84 Evo System Solver grid holding 2x plus 3y equals 12 and x minus y equals 1
  6. Press SOLVE (the graph key again). The answer arrives on its own screen: x = 3 and y = 2.
    The TI-84 Evo System Solver solution screen showing x equals 3 and y equals 2

More than two equations

The SETUP screen goes up to 10 equations and 10 unknowns. Press SETUP (the window key), arrow the EQUATIONS and UNKNOWNS rows to 3, and the variables become x, y, z. Press NEXT and the grid grows a z column that fills in the same way. Here is x + y + z = 6, x − y + z = 2, 2x + y − z = 1 solved in one press:

The TI-84 Evo System Solver solving a three-equation system and returning x equals 1, y equals 2, z equals 3

Good to know

  • When there is no single answer. Parallel lines that never cross get No solution found. Two copies of the same line get a solution set in terms of one variable, like x = 2 − y.
    The TI-84 Evo System Solver reporting No solution found for a parallel system
  • Change a number without starting over. SYSTEM (the zoom key) on the answer screen goes back to the equations with your numbers still in place, so you can edit one and press SOLVE again. RESET on the grid, then 1:Reset Defaults, clears everything back to zero.
  • Solving one polynomial instead of a system. For a single quadratic or cubic, the grid has a separate app: how to use the Polynomial Root Finder on the TI-84 Evo.
  • Leaving the app. QUIT sits on the y= key and drops you back on the home screen. From there on flips between the home screen and the app grid.