Problem 72 - Calculus Single Variable

Question

The hyperbolic sine and hyperbolic cosine functions are defined by $$ \cosh (x)=\frac{e^{x}+e^{-x}}{2} $$ and $$ \sinh (x)=\frac{e^{x}-e^{-x}}{2} $$. Express \(\cosh ^{\prime}(x)\) in terms of \(\sinh (x)\) and \(\sinh ^{\prime}(x)\) in terms of \(\cosh (x)\).

Step-by-Step Solution

Answer

The derivative of \( \cosh(x) \) is \( \sinh(x) \), and the derivative of \( \sinh(x) \) is \( \cosh(x) \).

Step 1: Write the Definition of Hyperbolic Cosine

The definition of the hyperbolic cosine function is given by \( \cosh(x) = \frac{e^x + e^{-x}}{2} \). This will be differentiated to find its derivative.

Step 2: Differentiate Hyperbolic Cosine

Differentiate \( \cosh(x) = \frac{e^x + e^{-x}}{2} \) with respect to \( x \). Using basic differentiation rules, the derivative of \( e^x \) is \( e^x \) and the derivative of \( e^{-x} \) is \( -e^{-x} \). Therefore, \[ \cosh'(x) = \frac{d}{dx} \left( \frac{e^x + e^{-x}}{2} \right) = \frac{1}{2}(e^x - e^{-x}) = \sinh(x). \]

Step 3: Write the Definition of Hyperbolic Sine

The definition of the hyperbolic sine function is given by \( \sinh(x) = \frac{e^x - e^{-x}}{2} \). We will differentiate this next to find its derivative.

Step 4: Differentiate Hyperbolic Sine

Differentiate \( \sinh(x) = \frac{e^x - e^{-x}}{2} \) with respect to \( x \). Using the differentiation rules as before, the derivative becomes: \[ \sinh'(x) = \frac{d}{dx} \left( \frac{e^x - e^{-x}}{2} \right) = \frac{1}{2}(e^x + e^{-x}) = \cosh(x). \]

Key Concepts

Hyperbolic Sine

The hyperbolic sine function, denoted as \( \sinh(x) \), has an interesting mathematical form that distinguishes it from the regular sine function. It is defined as \( \sinh(x) = \frac{e^x - e^{-x}}{2} \), where \( e^x \) represents the exponential function. This formula captures the unique behavior of hyperbolic functions, which are related to exponential growth and decay rather than periodic oscillations like traditional trigonometric functions. Hyperbolic functions often arise in mathematical contexts involving hyperbolas, hence their name. They can be encountered in physics, especially in theories of relativity and areas involving hyperbolic geometry. Understanding \( \sinh(x) \) is crucial as it serves as a building block for more complex mathematical constructs. It's noteworthy that \( \sinh(x) \) has a derivative that directly ties it to the hyperbolic cosine function, another core hyperbolic concept.

Hyperbolic Cosine

The hyperbolic cosine function, symbolized as \( \cosh(x) \), serves a vital role in hyperbolic geometry and other mathematical applications. Defined by \( \cosh(x) = \frac{e^x + e^{-x}}{2} \), it differs significantly from the cosine function found in trigonometry. Instead of oscillating between 1 and -1, \( \cosh(x) \) offers a smooth, always positive curve that reflects principles of hyperbolic space. This function is continuously increasing and is symmetric around the y-axis, illustrating an important property called evenness. In various scientific fields, such as engineering and physics, \( \cosh(x) \) is utilized to model real-world phenomena that follow hyperbolic patterns. Differentiating \( \cosh(x) \) yields the hyperbolic sine function, showcasing an essential connection between these two hyperbolic functions.

Differentiation Rules

Differentiation is a fundamental concept in calculus, and the differentiation rules provide the tools to derive the rates at which functions change. These rules are equally applicable to hyperbolic functions like \( \sinh(x) \) and \( \cosh(x) \). When differentiating \( \sinh(x) = \frac{e^x - e^{-x}}{2} \), we apply the basic rule that states the derivative of \( e^x \) is \( e^x \), and the derivative of \( e^{-x} \) is \( -e^{-x} \). This results in \( \sinh'(x) = \cosh(x) \), linking hyperbolic sine back to hyperbolic cosine. Similarly, differentiating \( \cosh(x) = \frac{e^x + e^{-x}}{2} \) leads us to \( \cosh'(x) = \sinh(x) \). These differentiation rules not only help in calculating derivatives but also highlight the intrinsic relationship between the hyperbolic functions. Understanding these differentiation rules is crucial for solving differential equations and modeling dynamic systems in a range of scientific disciplines.