# Hyperbolic Functions

## The Essentials of Hyperbolic Functions

In the field of mathematics, there are special combinations of natural exponential functions that are just as significant as the commonly known trigonometric functions. These functions are referred to as hyperbolic functions and have their own distinct features and characteristics. In this article, we will delve into the fundamentals of hyperbolic functions, including their definitions, formulas, graphs, properties, identities, derivatives, integrals, inverses, and real-world applications.

### Defining Hyperbolic Functions

What exactly are hyperbolic functions? Essentially, they are the trigonometric functions of the hyperbola. Just like how the trigonometric functions are related to the unit circle, hyperbolic functions are related to the unit hyperbola. They are defined in terms of the natural exponential function (e^x, where e is Euler's number), and their fundamental formulas are the hyperbolic cosine and hyperbolic sine.

Based on these two definitions, we can derive the remaining six main hyperbolic functions, which are shown in the table below.

### Hyperbolic Functions: Formulas

The formulas for the six main hyperbolic functions are:

• Hyperbolic secant (sech) = 1/cosh
• Hyperbolic cosecant (csch) = 1/sinh
• Hyperbolic tangent (tanh) = sinh/cosh
• Hyperbolic cotangent (coth) = cosh/sinh
• Hyperbolic co-secant (sech) = csch/cosh
• Hyperbolic co-tangent (coth) = coth/sinh

It is worth noting that the last four functions have unique pronunciations, namely cinch, cosh, tanch, and coseech. These formulas can also be expressed in exponential form, similar to Euler's formula.

### Deriving the Exponential Forms

A significant similarity between hyperbolic and trigonometric functions is evidenced in Euler's formula, which can be manipulated to solve for cosine and sine and provide us with the hyperbolic cosine and sine functions, respectively. However, the imaginary component of Euler's formula is not necessary in hyperbolic functions, as it does not play a role in their calculation.

### Hyperbolic Functions: Graphs

Using graphical addition, we can sketch the graphs of the two fundamental hyperbolic functions, hyperbolic cosine and hyperbolic sine. The graphs of the other six main hyperbolic functions involve horizontal and vertical asymptotes. Additionally, the hyperbolic secant has a global maximum at the point (0,1).

### Domain and Range of Hyperbolic Functions

While studying the graphs of hyperbolic functions, we can also determine their domains and ranges. This information is crucial in comprehending the behavior and limitations of these functions.

### Hyperbolic Functions: Properties and Identities

Similar to their trigonometric counterparts, hyperbolic functions possess various properties and identities that aid in solving equations and simplifying expressions. Some of these include the complementarity identities, double angle formulas, and product-to-sum formulas. It is vital to understand and apply these properties when working with hyperbolic functions.

### Putting Our Understanding to the Test

Let us test our knowledge of hyperbolic function identities. Can we prove equations (a) and (b) below?

(a) cosh^2(x) - sinh^2(x) = 1

(b) tanh(x) = sinh(x)/cosh(x)

Solution:

(a) We can begin by substituting the definitions of hyperbolic cosine and sine and simplifying the equation:

cosh^2(x) - sinh^2(x) = (e^x + e^-x)^2 - (e^x - e^-x)^2 = e^2x + 2 + e^-2x - (e^2x - 2 + e^-2x) = 1

(b) Using the proof from part (a), we can divide both sides by cosh(x) to get:

tanh(x) = sinh(x)/cosh(x) = (e^x - e^-x)/(e^x + e^-x) = (e^2x - 1)/(e^2x + 1) = (e^2x + 2 - 2)/(e^2x + 1) = 1 - 2/(e^2x + 1) = sinh(x)/cosh(x)

This example provides us with insight into the origin of the term "hyperbolic." It is fascinating to observe the similarities and differences between trigonometric and hyperbolic functions.

### The Relationship Between Trigonometric and Hyperbolic Functions

Let's consider a real number, x. If we plot the point (cos(x), sin(x)) on the unit circle, the coordinates correspond to the x and y values (cosine and sine). This representation can also be visualized as the angle x on the circumference of the circle, which represents twice the area of the shaded section.

## Understanding Hyperbolic Functions

Hyperbolic functions, also known as hyperbolic trigonometric functions, are the equivalent of trigonometric functions but defined using a hyperbola instead of a circle. This unique feature makes them a fascinating and practical concept in mathematics. In fact, they are often referred to as "circular functions" because of their connection to circles.

Similar to how a point on the unit circle can be represented as (cos(x), sin(x)), a point on the right half of the unit hyperbola can be represented as (cosh(x), sinh(x)). However, in this case, x does not represent an angle but twice the area of the shaded hyperbolic section. This concept highlights the relationship between these two sets of functions.

### The Derivatives of Hyperbolic Functions

Just like the trigonometric functions, the derivatives of hyperbolic functions have a close resemblance. These derivative formulas are useful in solving differential equations and finding the slope of a curve at a given point.

## Hyperbolic Functions: The Basics

In total, there are 6 hyperbolic functions: hyperbolic sine, hyperbolic cosine, hyperbolic tangent, hyperbolic cosecant, hyperbolic secant, and hyperbolic cotangent. These functions have similar properties and identities to the 6 trigonometric functions.

Let's delve into these functions and their derivatives in more depth.

## The Derivatives of Hyperbolic Functions

The table below lists the derivatives of hyperbolic functions. However, it's crucial to note that the derivatives of hyperbolic cosine and hyperbolic secant have opposite signs compared to their trigonometric counterparts. This is an important factor to keep in mind while differentiating these functions.

## The Chain Rule and Hyperbolic Functions

The differentiation rules for hyperbolic functions can also be combined using the Chain Rule, simplifying the process of finding the derivatives of more complex equations.

## Integrals of Hyperbolic Functions

The integrals of hyperbolic functions are analogous to their trigonometric counterparts. The table below lists these integrals for reference. Additionally, there are other useful integrals of hyperbolic functions that can be helpful in solving problems.

## Inverse Hyperbolic Functions

Based on the graphs of hyperbolic functions, we can see that hyperbolic cosine and hyperbolic secant are not one-to-one functions, unlike their counterparts. Therefore, to define their inverses, their domains must be restricted.

By doing so, we can define the inverse hyperbolic functions: arcosh, arsinh, artanh, arccsch, arcsech, and arccoth. Their formulas involve logarithmic functions, as logarithms are the inverse of exponential functions.

For instance, let's examine the derivation of arc sinh:

• Suppose we have ex = y
• Applying the definition of hyperbolic sine, sinh x = (ex - e-x)/2 = y
• Solving for ex:
• ex = y + (y2 + 1)/2
• Multiplying both sides by 2:
• 2ex = 2y + y2 + 1
• Now, using the quadratic formula to solve for ex:
• ex = (-y ± √(y2 + 1))/2
• Since ex is always positive, the only valid solution is:
• ex = (-y + √(y2 + 1))/2
• Taking the natural logarithm of both sides:
• x = ln [(-y + √(y2 + 1))/2]
• This shows that the inverse of sinh is ln [(-y + √(y2 + 1))/2]

## The Graphs of Inverse Hyperbolic Functions

The graphs of inverse hyperbolic functions are displayed below. It's crucial to note that inverse hyperbolic cosecant, secant, tangent, and cotangent have horizontal and/or vertical asymptotes, while the graphs of inverse hyperbolic cosine and inverse hyperbolic secant start at x=1. While studying these graphs, it is also essential to note the domains and ranges of each inverse hyperbolic function.

## The Derivatives of Inverse Hyperbolic Functions

Just like the hyperbolic functions themselves, all the inverse hyperbolic functions are differentiable. The derivatives of inverse hyperbolic functions are listed below for reference. We have previously shown the proof for the derivative of arc sinh.

## Real-Life Applications of Hyperbolic Functions

Hyperbolic functions, with their unique ties to hyperbolas, have numerous practical uses in the real world. Here are some examples of where these functions can be found:

• Describing the decay rates of light, velocity, electricity, or radioactivity
• Modeling the movement of waves on water
• Representing the shape of hanging wires, known as catenaries

One of the most notable applications of hyperbolic functions is in the study of catenary curves.

## Key Points to Remember about Hyperbolic Functions

Hyperbolic functions are a unique and fascinating concept in mathematics, as they are based on the trigonometric functions of hyperbolas. With 6 functions that are analogous to their trigonometric counterparts, we can analyze their derivatives, integrals, inverse functions, and practical uses for a better understanding of this topic.

## The Fundamentals of Hyperbolic Functions

If you have ever wanted to learn how to evaluate hyperbolic functions, you're in the right place. In this article, we will go through the process step by step, making it simple to comprehend and apply in any academic or professional setting.

## Evaluating Hyperbolic Functions

To evaluate a hyperbolic function, the first step is to substitute the desired value for the variable, typically represented by "x". You can then simplify the function using basic algebraic rules, arriving at the final result of the evaluated value.

## Practical Uses of Hyperbolic Functions

Hyperbolic functions have many applications in the fields of engineering and physics. They are particularly useful in studying the behavior of waves and vibrations in elastic materials. These functions can also aid in creating models for hanging cables and designing arches for structural stability.

## How to Write a Hyperbolic Function

Writing a hyperbolic function is similar to writing a trigonometric function for a circle. There are six main hyperbolic functions, each with its unique formula:

• sinh = (ex - e-x)/2
• cosh = (ex + e-x)/2
• tanh = (sinh x)/(cosh x)
• csch = 1/(sinh x)
• sech = 1/(cosh x)
• coth = (cosh x)/(sinh x)

By mastering these formulas, you will have a solid foundation for working with hyperbolic functions and their various applications.