Chapter 4: Problem 49
Find f such that: $$ f^{\prime}(x)=x^{2}-4, \quad f(0)=7 $$
Short Answer
Expert verified
The function is \( f(x) = \frac{x^3}{3} - 4x + 7 \).
Step by step solution
01
Identify the Integral
The problem gives us the derivative of the function, which is \( f'(x) = x^2 - 4 \). To find \( f(x) \), we need to integrate \( f'(x) \). Thus, \[ f(x) = \int (x^2 - 4) \, dx \]
02
Integrate the Function
Integrate the expression \( x^2 - 4 \) term by term. The integral of \( x^2 \) is \( \frac{x^3}{3} \), and the integral of \(-4\) is \(-4x\). Including the constant of integration \( C \), we have: \[ f(x) = \frac{x^3}{3} - 4x + C \]
03
Use the Initial Condition
We use the initial condition \( f(0) = 7 \) to find the constant \( C \). Substituting \( x = 0 \) into the integrated function, we get: \[ f(0) = \frac{0^3}{3} - 4(0) + C = 7 \]This simplifies to \( C = 7 \).
04
Write the Final Function
Substitute \( C = 7 \) back into the function from Step 2. Thus, the function \( f(x) \) is:\[ f(x) = \frac{x^3}{3} - 4x + 7 \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integration Techniques
Integration techniques are methods used to determine the antiderivative of a function. In this exercise, we start with the derivative, which is given as \( f'(x) = x^2 - 4 \). To find the original function \( f(x) \), we need to perform integration.
- Term-by-Term Integration: This technique involves integrating each term of the function separately. Here, we have two terms: \( x^2 \) and \( -4 \).
- Power Rule: The integral of \( x^n \) is \( \frac{x^{n+1}}{n+1} \). Applying this to \( x^2 \), we get the integral \( \frac{x^3}{3} \).
- Constant Rule: The integral of a constant \( a \) is \( ax \). So, for \( -4 \), the integral is \( -4x \).
- Constant of Integration: When performing indefinite integration, always add a constant \( C \) to your result. This accounts for any horizontal shifts in the original function.
Initial Value Problem
An initial value problem involves finding a function given its derivative and an initial condition. This exercise included that initial condition as \( f(0) = 7 \).
- Determine the Constant: To find \( C \), we substitute the initial values into the integrated function.
- Calculating with the Initial Condition: We use \( f(0) = 7 \) and substitute \( x = 0 \) into our integrated function. This gives us \( 0 + 0 + C = 7 \), leading to \( C = 7 \).
Antiderivative
The antiderivative, often symbolized as the indefinite integral, represents the original function whose derivative is known. Here, we were tasked with finding the antiderivative of \( f'(x) = x^2 - 4 \).
- Reverse Operation: Whereas differentiation involves finding the rate of change, integration seeks to 'reverse' this process by finding the original function.
- Building the Antiderivative: Through integration, each component of the expression is transformed back to its antecedent form. From \( x^2 \), we derive \( \frac{x^3}{3} \); from \(-4\), we ever so systematically deduce \(-4x\).
- Incorporating Constants: The constant \( C \) is intrinsic to the general form of an antiderivative and influenced by boundary or initial conditions provided. In this context, \( f(0) = 7 \) specified \( C \) concretely as 7.