The Christmas Equation

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I recently posted the following on this year's FPM Piazza forum.

Hi everyone,

I saw this a few years ago on QI, and found another version on the web at

http://mathandmultimedia.com/2014/12/02/merry-christmas-equation/

If we are told that

y=ln(xm−sa)r2

multiplying by r2 gives

yr2=ln(xm−sa).

Then taking e to the power of both sides gives

eyr2=xm−sa,

and multiplying both sides by m gives

meyr2=x−msa,

which can be rewritten as

merry=x−mas.

(And a Happy New Year!)

Best wishes,

Dr Feinstein

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