Multiplying Negative Numbers with Rectangles

I love using rectangles as a model for multiplication. In this video, Mike & son offer a pithy demonstration of WHY a negative number times a negative number has to come out positive:

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4 thoughts on “Multiplying Negative Numbers with Rectangles

  1. James Tanton has a video that does the same thing on a whiteboard, just drawing the rectangles, but I think it’s even more magical to see it acted out with the blocks.

  2. That’s really neat! Really shows why in this case minus X minus has to be a plus.

    I must use manipulatives to represent the grid method for multiplication in class!

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