Chapter 3: Problem 70
For the following exercises, the given limit represents the derivative of a function \(y=f(x)\) at \(x=a .\) Find \(f(x)\) and \(a .\) $$\lim _{h \rightarrow 0} \frac{\cos (\pi+h)+1}{h}$$
Short Answer
Expert verified
Function: \(f(x) = \cos(x) + 1\), Point: \(a = \pi\).
Step by step solution
01
Recognize the Limit Definition of the Derivative
The limit given, \( \lim_{h\rightarrow 0} \frac{\cos(\pi+h)+1}{h}\), represents the definition of the derivative of a function \( f(x) \) at a point \( a \). The general formula for the derivative using limits is \( f'(a) = \lim_{h \to 0} \frac{f(a+h) - f(a)}{h} \).
02
Identify the Function and Point
From the limit expression \( \frac{\cos(\pi+h)+1}{h} \), we can see that the term \( \cos(\pi + h) \) suggests a function involving cosine. Set \( f(x) = \cos(x) + 1 \). Therefore, the point \( a \) where the derivative is evaluated must be where \( x \) in \( \cos(x) + 1 \) is replaced by \( \pi \).
03
Verify the Function and Point
For \( f(x) = \cos(x) + 1 \), let's verify: \( f(\pi + h) = \cos(\pi + h) + 1 \). The derivative expression becomes \( \lim_{h\rightarrow 0} \frac{f(\pi + h) - f(\pi)}{h} \). We know \( f(\pi) = \cos(\pi) + 1 = -1 + 1 = 0 \), therefore, \( \frac{\cos(\pi + h) + 1 - 0}{h} \) matches the original limit.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative
Derivatives are vital in calculus because they quantify how a function changes at any given point. In simple terms, a derivative measures the slope of a function's graph at a particular point. This slope indicates the rate of change, which can be used for understanding growth patterns, motion, and various other time-dependent processes in mathematics and science.
Proficiency in derivatives is crucial for solving complex calculus problems and modeling real-world situations. The derivative of a function is often denoted by \( f'(x) \) or \( \frac{dy}{dx} \), and its computation can vary based on the context.
Proficiency in derivatives is crucial for solving complex calculus problems and modeling real-world situations. The derivative of a function is often denoted by \( f'(x) \) or \( \frac{dy}{dx} \), and its computation can vary based on the context.
Limit Definition
The limit definition of a derivative is a foundational concept in calculus. It provides a way to precisely calculate the derivative of a function. This is achieved by analyzing how the function behaves as it approaches a particular point.
The formal definition is: \[ f'(a) = \lim_{h \to 0} \frac{f(a+h) - f(a)}{h} \]Here’s how it works:
The formal definition is: \[ f'(a) = \lim_{h \to 0} \frac{f(a+h) - f(a)}{h} \]Here’s how it works:
- \( h \) is a small increment approaching zero.
- \( f(a+h) - f(a) \) represents the change in the function’s value over the interval \( h \).
- The entire expression gives the instantaneous rate of change, or the derivative at \( x = a \).
Trigonometric Functions
Trigonometric functions like sine and cosine frequently appear in calculus due to their repetitive and wave-like characteristics. These functions are often used to model oscillations and other cyclical phenomena.
The cosine function is defined as the horizontal coordinate of a point on the unit circle. For example, \( \cos(\pi + h) \) indicates the cosine of an angle formed by adding a small increment \( h \) to the angle \( \pi \).
Importantly, trigonometric functions have powerful derivative properties:
The cosine function is defined as the horizontal coordinate of a point on the unit circle. For example, \( \cos(\pi + h) \) indicates the cosine of an angle formed by adding a small increment \( h \) to the angle \( \pi \).
Importantly, trigonometric functions have powerful derivative properties:
- The derivative of \( \cos(x) \) is \( -\sin(x) \).
- These derivatives are useful for resolving rates of change in cyclic systems.
Problem Solving Steps
Approaching calculus problems effectively requires a systematic method of solving. Detailed problem-solving steps guide you to break down complex tasks into manageable parts. Here’s a general approach:
- **Identify the Problem**: Understand what is being asked. For example, you need to determine which function a given limit represents.
- **Apply the Limit Definition**: Use the definition to rewrite expressions. Determine how the function behaves as the change \( h \) approaches zero.
- **Substitute and Simplify**: Plug in known values or expressions to simplify the limit equation further. Simplifying is key to revealing recognizable patterns.
- **Verify Results**: Double-check calculations to ensure accuracy. Verification with the original problem can confirm if the conclusions make sense.