Problem 55 - Essential Calculus

Question

Find the derivative of the function. \(y=\sinh ^{-1}(\tan x)\)

Step-by-Step Solution

Answer

The derivative of \( y= \sinh^{-1}(\tan x) \) is \( y'= \frac{\sec^{2}(x)}{\sqrt{1+ \tan^{2}(x)}}\).

Step 1: Find the derivative of the outer function

Apply the formula for the derivative of the inverse hyperbolic sine function, \(f'(x)=(1/ \sqrt{1+x^{2}})*g'(x)\). Where, x is the argument of the sin function which in this case is \(\tan x\) and g'(x) is its derivative.

Step 2: Find the derivative of the inner function

The derivative of \( \tan x \) is \( \sec^{2}(x) \).

Step 3: Apply the chain rule

The chain rule states that the derivative of a composite function is the derivative of the outer function at the inner function times the derivative of the inner function. Therefore, the derivative of \( y \) is equal to \( \frac{\sec^{2}(x)}{\sqrt{1+ \tan^{2}(x)}}\).

Key Concepts

Chain Rule

The chain rule is a crucial tool in calculus for finding the derivative of composite functions. A composite function is essentially a function inside another function. Here's how the chain rule works:

• First, identify the outer function and the inner function in your composite function.
• The chain rule formula is: if you have a composite function \( f(g(x)) \), then its derivative \( f'(g(x)) \cdot g'(x) \).

In our exercise, we're dealing with the composite function \( y = \sinh^{-1}(\tan x) \), so:

• The outer function is \( \sinh^{-1}(u) \), and
• The inner function is \( \tan(x) \).

This means we first differentiate the outer function concerning its argument \( u \), which is \( \tan x \), and then multiply by the derivative of the inner function, \( \sec^2(x) \). This combination is what effectively provides the final derivative of the composite function. The chain rule beautifully ties together both parts, allowing us to find derivatives even in complex scenarios.

Inverse Trigonometric Functions

Inverse trigonometric functions, such as \( \sinh^{-1}(x) \), are functions that "undo" what the regular trigonometric functions do. For instance, while \( \sinh(x) \) maps an angle to a number, \( \sinh^{-1}(x) \) maps a number back to an angle.

These functions have specific ways to be differentiated. For \( \sinh^{-1}(x) \), the differentiation results in:

\[ \frac{d}{dx} \sinh^{-1}(x) = \frac{1}{\sqrt{1 + x^2}} \]

In our exercise, we applied this formula not directly to \( x \) but to \( \tan x \). Therefore, the structure of the formula adapts, incorporating the chain rule to also cover the derivative of \( \tan x \), resulting in a more comprehensive understanding and application when paired with the chain rule.

Hyperbolic Functions

Hyperbolic functions resemble trigonometric functions but are related to hyperbolas rather than circles. Functions like \( \sinh(x) \) and \( \cosh(x) \) are similar in name and form to \( \, \sin(x) \) and \( \cos(x) \), but they have distinct properties and applications.

• Hyperbolic sine, \( \sinh(x) \), is defined as \((e^x - e^{-x})/2\).
• These functions are important in areas involving hyperbolic geometry or applications like hanging cables in physics.

In this exercise, we utilized the inverse of the hyperbolic sine function, \( \sinh^{-1}(x) \). Similar to trigonometric functions, these inverse hyperbolic functions have specific derivatives, which help in solving complex differentiation problems where hyperbolic functions are involved.

The inverse hyperbolic sine provides an approach to translating back from transformed hyperbolic scenarios, making them very valuable in calculus when analyzing and breaking down intricate equations.