Chapter 12: Problem 169
For the following exercises, use the definition of derivative \(\lim _{h \rightarrow 0} \frac{f(x+h)-f(x)}{h}\) to calculate the derivative of each function. $$f(x)=-2 x+1$$
Short Answer
Expert verified
The derivative of \(-2x + 1\) is \(-2\).
Step by step solution
01
Write the Definition of the Derivative
The definition of the derivative of a function \( f(x) \) at a point \( x \) is given by \( \lim_{h \to 0} \frac{f(x+h) - f(x)}{h} \). Here, \( f(x) = -2x + 1 \).
02
Substitute into the Definition
Substitute \( f(x) = -2x + 1 \) into the definition to find \( f(x+h) \):\[ f(x+h) = -2(x+h) + 1 = -2x - 2h + 1 \]
03
Compute the Difference
Subtract \( f(x) \) from \( f(x+h) \):\[ f(x+h) - f(x) = (-2x - 2h + 1) - (-2x + 1) = -2h \]
04
Formulate the Derivative Expression
Substitute \( f(x+h) - f(x) = -2h \) into the derivative definition:\[ \lim_{h \to 0} \frac{-2h}{h} \]
05
Simplify the Expression
Simplify the expression by dividing both numerator and denominator by \( h \):\[ \lim_{h \to 0} -2 = -2 \]
06
Evaluate the Limit
Evaluate the limit for \( h \to 0 \). Since \(-2\) is constant and not dependent on \( h \), the limit simplifies to \(-2\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding the Definition of Derivative
In calculus, the derivative of a function at a point tells us the rate at which the function value changes as its input changes. Imagine the derivative as a tool that helps us predict how fast or slow something is happening, like the speed of a car or the growth of a plant. The formal definition of the derivative is given as:\[ \lim _{h \rightarrow 0} \frac{f(x+h)-f(x)}{h} \]This formula may look a bit complex at first, but it's essentially finding the slope of the tangent line through a point on the function's curve.
- Top Part : The \( f(x+h)-f(x) \) calculates the change in the function’s output.
- Bottom Part : The \( h \) represents an incredibly small change in the input that approaches zero.
- Whole Limit: As \( h \) gets very close to zero, the formula captures the instantaneous rate of change.
The Role of the Limit Process
The limit process is a key concept in the calculation of derivatives and many other areas of calculus. Using limits, we aim to understand what happens to a function as its input approaches a particular value.
In the context of the derivative, the limit \( \lim_{h \to 0} \frac{-2h}{h} \) examines how the ratio of the change in the function over the change in its input behaves as \( h \) gets infinitely small. Here, the tricky part lies in the simplification and evaluation of the limit.
In the context of the derivative, the limit \( \lim_{h \to 0} \frac{-2h}{h} \) examines how the ratio of the change in the function over the change in its input behaves as \( h \) gets infinitely small. Here, the tricky part lies in the simplification and evaluation of the limit.
- Cancel the \( h \) : In the expression \( \frac{-2h}{h} \), we simplify by canceling out \( h \), leading to \( -2 \).
- Evaluate the limit: By recognizing that \(-2\) is constant, the limit of a constant remains the constant itself, leading to a derivative of \(-2\).
Conducting Function Analysis
Function analysis is the detailed study of a function's behavior. It involves understanding the various properties of the function and how they relate to the derivative.
When analyzing the function \( f(x) = -2x + 1 \), we discover it is a linear function, which means it forms a straight line when plotted on a graph. The derivative calculation confirms a constant rate of change.
When analyzing the function \( f(x) = -2x + 1 \), we discover it is a linear function, which means it forms a straight line when plotted on a graph. The derivative calculation confirms a constant rate of change.
- Slope: The derivative \(-2\) represents the slope of the line. In this context, it seems the line is decreasing as \( x \) increases.
- Intercept: The \(+1\) in the original function acts as the y-intercept, showing where the line crosses the y-axis.
- Consistency: Because linear functions have a constant rate of change, their derivatives are also constant.