Hyperbolic Functions

The two basic hyperbolic functions are:

sinh and cosh
(pronounced "shine" and "cosh")

sinh x = ex − e−x 2

cosh x = ex + e−x 2

They are not the same as sin(x) and cos(x), but are a little bit similar:

sinh vs sin function
sinh vs sin

cosh vs cos function
cosh vs cos

rope bridge

Catenary

One of the interesting uses of Hyperbolic Functions is the curve made by suspended cables or chains.

A hanging cable forms a curve called a catenary defined using the cosh function:

f(x) = a cosh(x/a)

Like in this example from the page arc length :

catenary graph

Other Hyperbolic Functions

From sinh and cosh we can create:

Hyperbolic tangent "tanh" (pronounced "than"):

tanh x = sinh x cosh x = ex − e−x ex + e−x

tanh vs tan function
tanh vs tan

 

Hyperbolic cotangent:

coth x = cosh x sinh x = ex + e−x ex − e−x

 

Hyperbolic secant:

sech x = 1 cosh x = 2 ex + e−x

 

Hyperbolic cosecant "csch" or "cosech":

csch x = 1 sinh x = 2 ex − e−x

Why the Word "Hyperbolic" ?

Because it comes from measurements made on a Hyperbola:

tanh vs tan function

So, just like the trigonometric functions relate to a circle, the hyperbolic functions relate to a hyperbola.

Identities

And

Odd and Even

Both cosh and sech are Even Functions, the rest are Odd Functions.

Derivatives

Derivatives are:

d dx sinh x = cosh x

d dx cosh x = sinh x

d dx tanh x = 1 − tanh2 x