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Published on Aug 2, 2013
This video demonstrates multiplication with integers using a number line and representing multiplication as repeated addition. It is revealed that calculating the opposite (Additive Inverse) of a number is accomplished by multiplying the number by negative one. It should be mentioned to students that calculators have an opposite key labeled as (-) or (+/-) where pressing this key multiplies the quantity on the screen by negative one to calculate its opposite. The fact that "the opposite of a negative number is always positive" is used to explain the reasoning behind why a "negative times a negative" must be positive.