Chapter 4: Problem 28
Suppose that \(f(0)=5\) and that \(f^{\prime}(x)=2\) for all \(x .\) Must \(f(x)=\) \(2 x+5\) for all \(x ?\) Give reasons for your answer.
Short Answer
Expert verified
Yes, \(f(x)=2x+5\) for all \(x\).
Step by step solution
01
Consider the Information Given
We are given that \( f(0) = 5 \) and \( f'(x) = 2 \) for all \( x \). This tells us that the function \( f(x) \) has a constant derivative of 2, which means it is a linear function where the slope is 2.
02
Set Up the General Equation
Since the derivative is constant \( f'(x) = 2 \), the function \( f(x) \) must be of the form \( f(x) = 2x + C \), where \( C \) is a constant that we need to determine.
03
Solve for the Constant \(C\)
Use the information \( f(0) = 5 \) to find \( C \). Substituting \(x = 0\) into \( f(x) = 2x + C \), we have \( f(0) = 2(0) + C = 5 \). This simplifies to \( C = 5 \).
04
Write the Specific Equation
Having found \( C = 5 \), substitute back into the equation \( f(x) = 2x + C \) to get the specific function \( f(x) = 2x + 5 \).
05
Confirm Consistency
Check if \( f'(x) \) for \( f(x) = 2x + 5 \) equals 2 for all \( x \). Taking the derivative, \( f'(x) = 2 \), which matches the given \( f'(x) = 2 \). Therefore, \( f(x) = 2x + 5 \) is consistent with all given information.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative
In calculus, the derivative of a function represents how the function's output changes as its input changes. It's essentially the "rate of change" or "slope" of the function at any given point. For a linear function, the derivative is a constant, matching the slope of the line. For example, if you have a function like \( f(x) = 2x + 5 \), its derivative is simply \( f'(x) = 2 \).
This tells us that for every 1 unit increase in \(x\), \(f(x)\) increases by 2 units.
In this scenario, knowing that \( f'(x) = 2 \) for all \( x \) confirms that \( f(x) \) must be linear. The consistent derivative across all values of \( x \) indicates that the slope of the function never changes.
This tells us that for every 1 unit increase in \(x\), \(f(x)\) increases by 2 units.
In this scenario, knowing that \( f'(x) = 2 \) for all \( x \) confirms that \( f(x) \) must be linear. The consistent derivative across all values of \( x \) indicates that the slope of the function never changes.
- The derivative tells us how steep the function is.
- For linear functions, the derivative is always the same.
- A constant derivative implies a straight line.
Linear Function
A linear function is one of the simplest types of functions you'll encounter in mathematics. Its general form is \( f(x) = mx + b \), where \( m \) is the slope and \( b \) is the y-intercept. In the case of our problem, \( f(x) = 2x + 5 \) is a perfect example of a linear function with \( m = 2 \) and \( b = 5 \).
Some characteristics of linear functions include:
Some characteristics of linear functions include:
- They form straight lines when graphed.
- The slope \( m \) dictates how steep the line is.
- The y-intercept \( b \) shows where the line crosses the y-axis.
Constant
Constants in functions are values that do not change; they remain the same no matter what value the input \(x\) takes. In our exercise, the constant \( C \) was determined using the condition \( f(0) = 5 \).
Let's explore constants further:
It ensures that the function correctly represents the given information and maintains its structure across all \( x \) values.
Let's explore constants further:
- In a linear function like \( f(x) = 2x + C \), the \( C \) value indicates the y-intercept.
- For \( f(0) = 5 \), substituting \( x = 0 \) into \( f(x) = 2x + C \) results in \( C = 5 \).
- This means the function intersects the y-axis at 5.
It ensures that the function correctly represents the given information and maintains its structure across all \( x \) values.