Wednesday, September 05, 2007

laugh-a-day

A pure and an applied mathematician are asked to calculate
2 * 2.


*The applied mathematician's solution:


We have
2 * 2 = 2 *1/(1-1/2).

The second factor on the right hand side has a geometric series expansion

1/(1-1/2) = 1 + 1/2 +1/4 + 1/8 + ....

Cutting off the series after the second term yields the approximate solution

2 * 2 = 2 *(1 +1/2) = 3.


*The pure mathematician's solution:

We have

2 * 2 = (-2) *1/(1-3/2).

The second factor on the right hand side has a geometric series expansion

1/(1-3/2) = 1 + 3/2 +9/4 + 27/8 + ...,
which diverges.

Hence, the solution to 2 * 2 does not exist



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