Problem
Simplify the 7 upward flips
Flips cancel in pairs and 7 = 2×3 + 1, so 7 upward flips have the same effect as a single upward flip.
An odd number of identical flips acts like just one flip.
4.G.A.3Look For A PatternUndo the last move first: turn back 90 degrees counterclockwise
Reverse the last move: turn the shown numeral-4 figure 90 degrees counterclockwise.
To unwind moves you reverse the order and reverse each move - a clockwise turn is undone by a counterclockwise turn.
4.MD.C.5Work BackwardsWorking backward, the first move to undo is the last one applied - the 90-degree clockwise turn - and it is undone by turning the figure 90 degrees counterclockwise.
Why?
To rebuild the start you retrace the moves in reverse, so the newest move (the clockwise turn) is peeled off first, and a turn is peeled off by turning back the same amount the opposite way.
Why?
Spinning every point around the center one way and then the same amount the other way carries each point back along its path to exactly where it started.
Why?
Clockwise and counterclockwise are opposite directions, so an equal turn each way cancels out and leaves the figure unmoved.
Why?
Every move that changes a figure has an opposite move that reverses it, and for a turn the opposite move is an equal turn the other way.
Undo the flips: flip upward once
A flip is its own undo, so flip the figure upward once. The result is the original shape.
A flip reverses a flip, so one upward flip undoes the odd number of upward flips.
4.G.A.3Work BackwardsDraw the original
On the shown figure, turn it 90 degrees counterclockwise, then flip it upward once; draw that on the empty left grid.
Performing the reversed moves in reverse order reconstructs the start exactly.
4.G.A.3Draw A DiagramTo go back to the start, undo the moves in reverse: turn it back the other way, then flip it once - reversing moves is just Grade 4 flip-and-turn thinking!
- Simplify the 7 upward flips
- Undo the last move first: turn back 90 degrees counterclockwise
- Undo the flips: flip upward once
- Draw the original