How to solve an equation that spells Merry Christmas?

December 2, 2015 1:26 PM

I'm teaching my last class of term tomorrow. I found this image on the Chive ( Number 23, here. A professor solves an algebraic problem that spells Merry Christmas. I can follow every step but that from #2 to #3. "Ln" seems to become "Cn" and I don't know why. Might someone please write it out for me? Thank you and Merry Christmas!
posted by holdenjordahl to Education (7 answers total)

I don't know myself, but here's a thread on it from r/math a year ago.
posted by phunniemee at 1:34 PM on December 2, 2015

In both cases it is "ln", i.e. the natural logarithm.
posted by RichardP at 1:34 PM on December 2, 2015 [6 favorites]

Pretty sure it doesn't change, he just wrote the L weird on the 2nd line by accident. From step 2-3 he raises both sides as exponents of e which gets rid of the ln on the right and does the e^r2y thing on the left - that wouldn't work if it had changed to something other than ln.
posted by brainmouse at 1:34 PM on December 2, 2015 [3 favorites]

The "Ln" doesn't change to "Cn". That wouldn't mean anything. It's just that the "L" got a little curly in line #3.
posted by JimN2TAW at 1:38 PM on December 2, 2015 [1 favorite]

brainmouse has it -- the ln disappears through exponentiation, it never changes to ch.
posted by forza at 1:59 PM on December 2, 2015 [1 favorite]

Response by poster: Got it. Thanks everyone!
posted by holdenjordahl at 3:22 PM on December 2, 2015

Re #18 in that link, in junior high I embarrassed myself doing that test in front of a whole class full of fellow smarty pants.
posted by intermod at 9:12 PM on December 2, 2015