ei*x = cis(x)
simply relates the transcendental functions of exponentiation and trigonometry. The statement given by inserting a value of pi for x demonstrates the uses of the natural exponentiation base e, pi, the negative unit, and the imaginary unit:
ei*pi = -1
Because it represents so many concepts in one small equality, it's part of the demonstration of intelligent life on Earth imprinted on the side of many NASA spacecraft. Of course, that assumes that the little green men will have the patience and luck enough to figure out that those little scrawlings represent mathematical truths and not a declaration of interstellar war.