How to Draw the Inverse of a Function on the TI-84 Plus

The big idea of inverse function is that x and y switch places. Your TI-84 Plus calculator has a built-in feature that enables you to "draw" the inverse of a function. Essentially, the calculator is "graphing" (not drawing) the inverse of the function.

However, unlike a graph, you can’t perform a trace or any other type of function evaluation on the drawn inverse. Another reason this term is used may be that the drawn inverse need not be a function.

Follow these steps to draw the inverse of a function:

1. Enter your functions in the Y= editor.

   See the first screen, which has Y₁ = e^xentered. This function has a mathematically famous inverse, f^–1(x) = ln(x).

   

2. Press [2nd][MODE] to access the Home screen.

3. Press [2nd][PRGM][8] to insert the DrawInv function

4. Press [ALPHA][TRACE] and choose the name of the function you entered.

   See the second screen.

5. Press [ENTER] to display the graph of your function and draw the inverse of your function.

   See the third screen.

   Enter Y₂ = ln(x) to double-check that the inverse your calculator drew is the natural log function. In the Y= editor, use the left-arrow key and press [ENTER] to change the line style. Then press [GRAPH] and enjoy the show!