by John on (#6CZKM)
Motivating examples The addition theorem for cosine says that and the addition theorem for hyperbolic cosine is analogous, though with a sign change. An addition theorem is a theorem that relates a function's value at x + y to its values at x and at y. The squaring function satisfies a very simple addition theorem [...]The post When does a function have an addition theorem? first appeared on John D. Cook.