Wednesday, June 24, 2009


The inverse of 1-x2 can be calcuated two ways.

First way: We know 1/(1-y)=(1+y+y2+y3+...) so substitute y=2x, and it comes out.

Second way: Do it directly.

  1. The constant coefficent must be 1.
  2. The x coefficient must 2.
  3. The x2 coefficient must 4.
  4. The x3 coefficient must 8.

We did a couple more examples of computing an inverse. Then we went to an interesting one.

What is the multiplicative inverse of 1-x-x2.

It turns out to be 1+x+2x2+3x3+5x4+8x5+13x6...

The coefficients are the fibonacci series!

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I'm research faculty at MIT, and Chief Architect at Tokutek.