Answered on Sep 10th, 2014 at 3:58 PM
Copyright requires a modicum of creativity. Further, copyright cannot be used to copyright functionality. On this basis, it is rare that a math equation fits within the bounds of copyrightable subject matter in the US.
I have a t-shirt from Think Geek (or someone comparable) that has a math equation on the front. There are four lines that are used to simplify/solve the equation and the last line reads "i <3 u" (I love you, if you don't see the heart). The math equations on the t-shirt could be copyright protected. The copyright would not be protecting the math function, and would be protecting a textual message utilizing a modicum of creativity.
Hope that helps,
Todd