Chapter 37: Problem 1
Determine the differential coefficient of: (a) th \(x\) (b) \(\operatorname{sech} x\)
Short Answer
Expert verified
(a) 0, (b)
-\operatorname{sech} x \tanh x
Step by step solution
01
Differentiate the Constant Function
The function given is a constant function denoted by \(a\). The derivative of a constant function \(f(x) = c\) is zero because \ \(\frac{d}{dx}c = 0\)\ Therefore, the differential coefficient of \(a\) with respect to \(x\) is \(0\).
02
Use the Chain Rule for \( \operatorname{sech} x\)
The hyperbolic secant function can be expressed as \( \operatorname{sech} x = \frac{1}{\cosh x} \). To differentiate \(\operatorname{sech} x\), we use the chain rule and the quotient rule. Start with the expression \( \operatorname{sech} x = (\cosh x)^{-1} \).
03
Differentiate \((\cosh x)^{-1}\)
Using the chain rule, differentiate \((\cosh x)^{-1}\) with respect to \(x\): \ \( \frac{d}{dx} (\cosh x)^{-1} = -1 \cdot (\cosh x)^{-2} \cdot \sinh x\) \ Simplify to get: \ \( -\frac{\sinh x}{\cosh^2 x}\).
04
Simplify Using Hyperbolic Identity
Apply the identity \(1 - \tanh^2 x = \operatorname{sech}^2 x\) and note that \(\sinh x / \cosh x = \tanh x\). Thus: \ \( \frac{\sinh x}{\cosh^2 x} = \tanh x \operatorname{sech} x\) \ Thus, the derivative of \(\operatorname{sech} x\) is: \(-\operatorname{sech} x \tanh x\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Derivatives
The concept of derivatives in calculus is fundamental. A derivative represents the rate at which a function changes as its input changes. Think of it as the "slope" of a function at any given point. Here are some key points about derivatives:
- The derivative of a constant function is zero. This is because constants do not change, which means their rate of change is zero.
- For example, if you have a function \( f(x) = c \), where \( c \) is a constant, then \( \frac{d}{dx}c = 0 \).
Exploring the Chain Rule
When dealing with complex functions, the chain rule is essential. The chain rule allows us to differentiate a function that is composed of other functions. Here's how it works:
- Consider a composite function \( f(g(x)) \). To find its derivative, we use the chain rule formula: \( \frac{df}{dx} = \frac{df}{dg} \cdot \frac{dg}{dx} \).
- This approach is useful when differentiating functions like \( \operatorname{sech} x = (\cosh x)^{-1} \).
Understanding Hyperbolic Functions
Hyperbolic functions are analogs of trigonometric functions but for hyperbolas. They have unique properties and identities:
- The hyperbolic secant function, \( \operatorname{sech} x \), is defined as \( \operatorname{sech} x = \frac{1}{\cosh x} \).
- To differentiate \( \operatorname{sech} x \), we use both the chain rule and hyperbolic identities, such as \( 1 - \tanh^2 x = \operatorname{sech}^2 x \).
- Understanding these identities helps simplify the differentiation process, as shown when simplifying \( \frac{\sinh x}{\cosh^2 x} \) to arrive at the derivative \( -\operatorname{sech} x \tanh x \).