We’ve Had It All Wrong

There have been quite a few blog posts lately discussing how one would explain to a “non-math” person why a negative times a negative is a positive. I think the reason we have such a hard time explaining it is because it’s not true.   We need look no further than California’s own Nancy Pelosi for the explanation. (Check right around 3:50)

In an interview with CNBC’s Maria Bartiromo, Pelosi was asked if the expiration of the Bush tax cuts would amount to a tax increase. 

Her response:

“It’s not a tax increase.  It is eliminating a tax decrease that was there.”

So there you have it–eliminating a decrease does not amount to an increase.  I had better go fix those lesson plans.   Thanks for clearing things up, Ms. Pelosi.


2 Responses to “We’ve Had It All Wrong”

  1. 1 peeterjoot December 4, 2009 at 10:37 am


    My personal best I ever did to explain this to myself was:

    multiplication by -1 is a rotation in space (ie. a vector space), or a reflection on a number line in a 1D space. Two such multiplications rotate or reflect back to the original position.

    This fails the criteria for explanation to a non-mathematician.

  2. 2 David Cox December 4, 2009 at 3:05 pm

    The vector works too. I always liked Stand and Deliver’s, “Fill the hole Johnny.”

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They don't know it yet, but I have more questions than they do.

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