The Christmas Equation

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I posted the following in December 2021 on my first-year pure module's 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

\qquad\displaystyle y=\frac{\ln(\frac{x}m-sa)}{r^2}

multiplying by r^2 gives

\qquad yr^2=\ln(\frac{x}m-sa)\,.

Then taking e to the power of both sides give

\qquad\displaystyle e^{yr^2}=\frac{x}m-sa\,,

and multiplying both sides by m gives

\qquad me^{yr^2}=x-msa\,,

which can be rewritten as

\qquad me^{rry}=x-mas\,.

(And a Happy New Year!)

Best wishes,

Dr Feinstein

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