::My draft of an explanation of how we ''really'' define sine, cosine, and exponential, and how we therefore ''really'' know that [[Euler's Formula]] and Euler's identity are true, without all the non-rigorous middle-school-level handwaving, will wait until I come back. | ::My draft of an explanation of how we ''really'' define sine, cosine, and exponential, and how we therefore ''really'' know that [[Euler's Formula]] and Euler's identity are true, without all the non-rigorous middle-school-level handwaving, will wait until I come back. |