Luckily, my AC circuits class was basically the applied version of this article, with lots of conversions between the complex and phase-amplitude descriptions.

Luckily, my AC circuits class was basically the applied version of this article, with lots of conversions between the complex and phase-amplitude descriptions. What blew my mind at the time was the exponential notation for the unit phasor: e^(i * x). It turns out that e^(i * x) = cos(x) + i * sin(x) because that's just the way the math works out, and it's trivial to work it out yourself by looking at the Taylor series expansions of the three terms.