don steward
mathematics teaching 10 ~ 16

Tuesday, 4 June 2013

multiplying directed numbers

using a grid can establish some rationale for the multiplication of two negative numbers being a positive number

this approach was suggested to me by Gill Hatch, when she was at Manchester Metropolitan University

a powerpoint goes through the solution steps
but it's probably better developed with student suggestions

firstly, using some examples of 5 (down) times 6 (across)
establish that the answer must be 30

eventually there may be a suggestion that involves two negatives (as in the 4th one)

knowing that the overall total must be 30 identifies the bottom right hand product needed to make this total

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