AYESHA RASCOE, HOST:
OK, so hold on, Will. Before we totally wrap up this week's puzzle, we need to admit to a bit of a mistake that we made in one of our answers last week. I think you know what I'm talking about.
WILL SHORTZ, BYLINE: Yeah. Yeah. And when you say we, that's very generous, but it was my mistake.
RASCOE: So here is what happened.
(SOUNDBITE OF ARCHIVED NPR BROADCAST)
SHORTZ: In math, what cosine is to sine.
ELIE DOLGIN: Inverse function.
SHORTZ: Inverse function is it.
RASCOE: OK, ah - so, as it turns out, that is not it. And y'all did not hesitate to give us a quick math lesson, specifically in trigonometry. Do you remember trigonometry, Will? I mean, I think I learned it either junior high or senior high or whatever high, but it was a long time ago. That's what I know. Do you remember that?
SHORTZ: Oh, I remember taking trigonometry, and obviously, I've forgotten part of it, too.
RASCOE: (Laughter) So we got a lot of emails on this, including one from Martha Hasting, a professor of engineering mathematics at Washington University in Saint Louis, Mo., so first off, what's the inverse of a function?
MARTHA HASTING: If two functions are inverses, that means that one reverses the action of the other.
RASCOE: And Professor Hasting said that the cosine function definitely does not do this for sine, so does sine even have an inverse function?
HASTING: There is a function which does always reverse the action of the sine function, and it's called the arcsine function.
RASCOE: All right, so I think I get it, or I'm going to pretend that I get it. Do you got it, Will?
SHORTZ: Oh, I got it. Yeah. I will try never to make that mistake again.
RASCOE: And to our listeners, thank you for keeping us on our toes. Transcript provided by NPR, Copyright NPR.
