Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In mathematics, a reflection formula or reflection relation for a function f is a relationship between f(a x) and f(x). It is a special case of a functional equation, and it is very common in the literature to use the term "functional equation" when "reflection formula" is meant. Reflection formulas are useful for numerical computation of special functions. In effect, an approximation that has greater accuracy or only converges on one side of a reflection point (typically in the positive half of the complex plane) can be employed for all arguments.