Bill Cosby the Mathematician

Leafing my way through the Chicago Reader, I came across this ad:


It took me a moment to sort it out. Can you?
And I don't even know what it is an ad for. Maybe he is coming to Chicago soon for a show? Maybe his greatgrandchild said "Hey, Great Grandpa, look what I learned in school today!" and BC was just so taken with the idea - and the fact that his own clever descendent came up with it, that he decided to run it as an ad.
In any case, generally I hate ads, but I sure like this one.

Ha! Or maybe it is old as can be (as in dating to at least 2011) and I am just catching up:

http://weknowmemes.com/2011/11/sin-b-tan-b-equals-cosby/ 

Well I've never pretended to keep up.