Undo, Undo

Lesson 2 of 12 · 7 min · Free, no account needed

What you will learn

Every step has an inverse operation that undoes it: + undoes −, × undoes ÷.
To undo a whole machine, undo its steps in reverse order: the last one on is the first one off.
The undo machine is the inverse function: it turns the output back into the input.

This machine gave out 23. What went in?
It multiplies by 3, then adds 2. Drag the marker to your bet.
Run the machine backwards.
Press Step back. Watch each station turn into its undo.
Build the undo machine.
Fill the undo belt with two chips. Check sends 23 through it, from right to left.
Undo in reverse order.
An inverse operation undoes another: −2 undoes +2, ÷3 undoes ×3.
To undo a machine, undo its steps in reverse order. Like socks and shoes: shoes go on last, so they come off first.
The whole undo machine is the inverse function: f(x) = 3x + 2 turns 7 into 23, and its inverse turns 23 back into 7.
This one gave 25. Find the input two ways.
First guess: turn the dial and Run forward. Then press Rewind. Pick the way that won.
Build your own lock.
Drag two or three stations onto the belt, then tap a secret number. The machine shows your lock code.
Game: crack the locks.
Tap the undo chips in order. A wrong chip sets off the alarm. You have 3 lives per lock.
This undo program should print 7. It prints 63.
It should undo y = 3x + 2 for y = 23. Fix one sign.
One station is tricky to undo.
This station squares its input. Tap 3 and −3, then press Rewind.

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