Chapter 14: Problem 11
Find a function \(f\) such that \(f^{\prime \prime \prime}(x)=1 / \sqrt{1+\sin ^{2} x}\). (This problem is supposed to be easy; don't misinterpret the word "find."
Short Answer
Expert verified
\( f(x) = \int \int \frac{1}{\sqrt{1 + \sin^2(x)}} \, dx \, dx + C_2 \frac{x^2}{2} + C_3 x + C_4 \).
Step by step solution
01
- Understand the Given Information
The problem provides the third derivative of a function, denoted as: \[ f^{\frac{1}{1}}(x) = \frac{1}{\sqrt{1 + \sin^2(x)}} \]
02
- Integrate the Third Derivative
To find the original function, integrate the third derivative to find the second derivative: \[ f^{\frac{1}{2}}(x) = \int \frac{1}{\sqrt{1 + \sin^2(x)}} \, dx \]. Let this integral be denoted as: \[ g(x) = \int \frac{1}{\sqrt{1 + \sin^2(x)}} \, dx \]. So, \[ f^{\frac{1}{2}}(x) = g(x) + C_1 \], where \( C_1 \) is the constant of integration.
03
- Integrate the Second Derivative
Next, integrate \( f^{\frac{1}{2}}(x) \) to find the first derivative: \[ f^{\frac{1}{1}}(x) = \int (g(x) + C_1) \, dx = \int g(x) \, dx + C_2 x + C_3 \], where \( C_2 \) and \( C_3 \) are additional constants of integration.
04
- Integrate the First Derivative
Finally, integrate \( f^{\frac{1}{1}}(x) \) to find the original function: \[ f(x) = \int (\int g(x) \, dx + C_2 x + C_3) \, dx \]. This yields: \[ f(x) = \int \int \frac{1}{\sqrt{1 + \sin^2(x)}} \, dx + C_2 \int x \, dx + C_3 \int 1 \, dx + C_4 \], where \( C_4 \) is another constant of integration.
05
- Combine in Final Form
Combine the results to get the original function: \[ f(x) = \int \left(\int \frac{1}{\sqrt{1 + \sin^2(x)}} \, dx\right) dx + C_2 \frac{x^2}{2} + C_3 x + C_4 \]. This represents the general form of the function \( f(x) \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Integration
Integration is the process of finding a function when its derivative is given. In this problem, we start with the third derivative of a function, which is expressed as: \[ f^{\frac{1}{1}}(x) = \frac{1}{\text{√}(1 + \text{sin}^2(x))} \] To retrieve the original function from this derivative, we need to integrate it three times. Each integration step reverses one derivative, gradually taking us closer to the original function. - In the first step, we integrate the third derivative to get the second derivative, denoted as \( f^{\frac{1}{2}}(x) \). - Then, we integrate the second derivative to obtain the first derivative, \( f^{\frac{1}{1}}(x) \). - Finally, we integrate the first derivative to find the original function, \( f(x) \).Remember, every time we integrate, we add a constant of integration, since the derivative of any constant is zero.
Third Derivative
The third derivative of a function indicates how the second derivative changes with respect to \( x \). In other words, it tells us about the concavity and the rate at which the curvature of the function is changing. Given the third derivative \( f^{\frac{1}{1}}(x) = \frac{1}{\text{√}(1 + \text{sin}^2(x))} \), we use integration to find the lower-order derivatives and ultimately the original function. The process follows these steps:
- First, integrate the third derivative to find the second derivative \( f^{\frac{1}{2}}(x) \).
- Second, integrate the second derivative to find the first derivative \( f^{\frac{1}{1}}(x) \).
- Third, integrate the first derivative to find the original function \( f(x) \).
Constant of Integration
In calculus, the constant of integration appears whenever we integrate a function. When differentiating, any constant term disappears, so integrating requires adding back an unknown constant to account for all possible original functions. For example, after integrating the third derivative \( \frac{1}{\text{√}(1 + \text{sin}^2(x))} \), we get: \[ f^{\frac{1}{2}}(x) = \text{∫} \frac{1}{\text{√}(1 + \text{sin}^2(x))} \text{dx} + C_1 \] Here, \( C_1 \) is the constant of integration. - The same process repeats for each subsequent integration, leading to more integration constants \( C_2, C_3, \) and \( C_4 \). - Each constant represents a level of freedom in the possible solutions for the function. Ultimately, the general solution is expressed as a combination of several integration constants, reflecting the family of functions that share the same derivatives up to the third order.