Hyperbolic Functions
The hyperbolic functions are defined in terms of certain combinations of and . These functions arise naturally in various engineering and physics applications, including the study of water waves and vibrations of elastic membranes. Another common use for a hyperbolic function is the representation of a hanging chain or cable, also known as a catenary.

The shape of a strand of silk in a spider’s web can be described in terms of a hyperbolic function. The same shape applies to a chain or cable hanging from two supports with only its own weight.
The hyperbolic sine and hyperbolic cosine are defined as
and
The other hyperbolic functions are then defined in terms of and .