One turn, then back
To undo one move, turn the same face the other way. R is the right face a quarter turn clockwise, so R prime puts it back. The same holds for every face.
A face turned twice is undone by turning it twice. R2 is undone by R2, and it does not matter which way you turn.
Undo the last move first
Make R, then U. The cube is now two moves from solved.
To put it back, undo the last move first. The last move was U, so make U prime. Then undo R with R prime. So R U is undone by U prime R prime.
The order matters. R prime U prime does not put the cube back, because it undoes the first move while the second one is still there.
Undo two moves
Someone makes F, then R. You want the cube back the way it was.
Work out which move you undo first, then choose the sequence.
Try it
Which sequence undoes F R?
- F' R'
- R' F'
Show the answer
R' F'
Correct. R was the last move, so R prime comes first, then F prime.
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