Sunday, October 25, 2009

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.


peeterjoot said...


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.

David Cox said...

The vector works too. I always liked Stand and Deliver's, "Fill the hole Johnny."