e to the pi times i
e to the pi times i
[Two Cueballs are standing at a board with writing on. One Cueball is pointing at the board.] Cueball: Numbers of the form n√-1 are "imaginary," but can still be used in equations. Friend: Okay. Cueball: And e^(π√-1)=-1. Friend: Now you're just fucking with me.

The comic largely references Euler's identity . This identity states that e iπ + 1 = 0. Therefore, e iπ = −1.
The humor from this comic is because of the seemingly arbitrary relationship between e, π, and the identity of i (the square root of −1). e is the mathematical identity of which the derivative of e x with respect to x is still e x , while π is the relationship between the circumference of a circle divided by its diameter. Taking these two values and applying them to the value of i in such a manner makes it seem counter-intuitive  that it would yield −1 from basic analysis. The above linked Wikipedia page goes into good detail of how to derive this identity, as does this YouTube video .
The title text refers to how Euler's identity is called upon in complex form (separating real and imaginary numbers): e ix = cos(x) + i sin(x).
[Two Cueballs are standing at a board with writing on. One Cueball is pointing at the board.] Cueball: Numbers of the form n√-1 are "imaginary," but can still be used in equations. Friend: Okay. Cueball: And e^(π√-1)=-1. Friend: Now you're just fucking with me.
