Comments on: Birthday Polynomials http://samjshah.com/2008/03/31/birthday-polynomials/ Wed, 15 Feb 2012 22:10:14 +0000 hourly 1 http://wordpress.com/ By: samjshah http://samjshah.com/2008/03/31/birthday-polynomials/#comment-39 Mon, 31 Mar 2008 10:44:50 +0000 http://samjshah.wordpress.com/?p=100#comment-39 Not quite! I want to use the birthdate of someone to create a polynomial which will–when you find the x-coordinate of the inflection point–be the student’s age. So the inflection point will be at (age, something).

So for the January 25, 1980 example, the x-coordinate of the inflection point of f(x)=(x+1980*3)(x-2008*3)(x)+1x+25 will be 28!

Inflection points (potentially) occur when the second derivative is equal to 0. So f”(x)=6x-1980*3*2+2008*3*2=6x-6(age). So the x-coordinate is the age.

(The birthdate and month are red herrings because when you take the second derivative it equals zero.)

Sorry this isn’t clear… I know it’s not… It was late and I was ready to pass out and this week is going to be tough and I wouldn’t have made time for it.

PS. I love the “given the points, find the parabola that fits it” thing.

]]> By: jd2718 http://samjshah.com/2008/03/31/birthday-polynomials/#comment-38 Mon, 31 Mar 2008 03:43:03 +0000 http://samjshah.wordpress.com/?p=100#comment-38 inflection points at (mm,dd) and (yy,yy)?

I don’t know, there’s lots of variations. I’ll stick with my precalc parabolas and my algebra triangles.

(until I teach calc, I guess)

Jonathan

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