Some Strange Circles

I was trying to construct a simple, introductory intersection problem for the first day of Calculus class, so I started with a well-behaved circle:

This is a circle centered at (3,2) with radius 5.  I picked two points on the circle, (0,6) and (7,-1), found the equation of the line between them, and put together my system of equations:

So I had successfully reverse-engineered my circle-and-line intersection problem with two nice solutions:  (0,6) and (7,-1).

Unfortunately, I made a typo on the handout.  At the end of the left side of the circle equation I wrote ” + 12″ instead of ” – 12″.

So all my work was for naught.  Or so I thought.  Turns out, at least two amazing things happen:

First, the new circle still ends up having a nice radius, namely 1.  What’s even more amazing is that the new circle also ends up having two nice intersections with the given line, (3,3) and (4,2)!

Strange Circles

I wish my intentional work always turned out as well as this mistake!

By patrick honner, ago

Tighter Airline Seats

new airline seatThere is an interesting article in the Times about a new kind of airline seat.  Amusingly called the SkyRider, it’s more squat than seat.  I think the look on this guy’s face says it all.

Not surprisingly, this is all about money–and a lot of it.  This seat has a pitch of 23 inches; pitch is airline jargon for the distance between a point on a seat and the identical point on the next seat, sort of like the wavelength of a wave.  On typical commercial aircraft, pitch is closer to 32 inches.  An airline could therefore install many more of these new seats, and of course, more seats means more tickets means more money.

For instance, on an aircraft with 20 rows of seats with a 32-inch pitc you could get almost 28 rows of SkyRiders in there.  That’s 8 extra rows, so about 48 extra tickets.  At two or three hundred dollaras per ticket, that’s a nice increase in revenue–on the order of an extra $10000 per flight.  You could even charge less for these seats and still make more money.

As bad as this sounds, it’s not nearly as objectionable as paying to use the bathroom on a plane.

By patrick honner, ago

Bagel-nomics

bagelI have a natural tendency toward the quantitative side of things.  That, together with a substantial history of employment in the food service industry, has doomed me to forever over-analyze menu prices.

I recently realized that my local bagel shop has been charging me an outrageous premium for premium cream cheese.  The cost of a bagel is 95 cents, and a bagel with cream cheese is $1.90; these are pretty standard prices around town.

But here’s the kicker:  a bagel with scallion cream cheese at this place is $3.25.  That’s an additional $1.35–not for the cream cheese, mind you, but for the upgrade of scallion cream cheese over plain cream cheese.

Scallions.  Scallions are like onion weeds.  I buy a bundle of ten of them for 40 cents, use three of them, and then toss the rest, probably because they’ve wilted within two days of purchase.  They are expendable stalks at the bottom of the vegetable pyramid–savory and crisp, yes, but almost literally a dime-a-dozen.  If anything, scallion cream cheese should be cheaper than plain cream cheese, because whatever volume of cream cheese is being replaced by the scallions is almost certainly more valuable than the scallions themselves.

The guys behind the counter seemed sympathetic to my argument, but they still charged me $3.25.

By patrick honner, ago

New Digits of Pi

piA computer scientist at Yahoo has used “cloud computing” to find the most distant digits yet of pi’s decimal expansion.

This new approach to networking machines and processors, allowing them to act as one super-computer rather than, say, 100 individuals, allowed this record-setting calculation to be in 23 days when, under normal circumstances, it would have taken nearly 500 years.

Apparently a similar approach at Google resulted in verifying that every configuration of the Rubik’s cube can be solved in 20 moves or less.

By patrick honner, ago

Football Inequality

The 2010 NFL season is off to a mathematically interesting start.

The Jets, Patriots, Bengals, and Ravens each have played two games against other teams in that group of four.  The results can be organized like this (for example, the Bengals lost to the Patriots but beat the Ravens)

AFC East InequalityNow, if we interpret “wins the game” to mean something like “is better than”, and if we believe that “is better than” is a transitive relationship (i.e. “If A is better than B and B is better than C, then A is better than C”), then the Jets are better than every team in their division, including themselves!  Some might prefer to say that they are even worse than themselves.

It’s not easy producing mathematically consistent ranking systems, but it’s an interesting and useful problem, and the field is quite rich.

By patrick honner, ago
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