Chapter 4: Problem 40
\(23-46\) Find \(f\) \(^{\prime \prime}(t)=3 / \sqrt{t}, \quad f(4)=20, \quad f^{\prime}(4)=7\)
Short Answer
Expert verified
The function is \( f(t) = 4t^{3/2} - 5t + 8 \).
Step by step solution
01
Integrate the Second Derivative
We start by integrating the given second derivative function, \( f''(t) = \frac{3}{\sqrt{t}} \). Rewriting \( \frac{3}{\sqrt{t}} \) as \( 3t^{-1/2} \), allows us to find the first derivative, \( f'(t) \), by integrating:\[ f'(t) = \int 3t^{-1/2} \, dt. \]The integral of \( 3t^{-1/2} \) is \( 6t^{1/2} + C_1 \). So, \( f'(t) = 6t^{1/2} + C_1 \).
02
Use Initial Condition on First Derivative
We apply the initial condition \( f'(4) = 7 \) to determine \( C_1 \).\[ f'(4) = 6(4)^{1/2} + C_1 = 7. \]Calculating \( 6 \times 2 + C_1 = 7 \), we get \( 12 + C_1 = 7 \). Solving for \( C_1 \), we find \( C_1 = -5 \). Thus, \( f'(t) = 6t^{1/2} - 5 \).
03
Integrate the First Derivative
Next, integrate \( f'(t) = 6t^{1/2} - 5 \) to find \( f(t) \):\[ f(t) = \int (6t^{1/2} - 5) \, dt. \]The integral becomes \( 4t^{3/2} - 5t + C_2 \). Thus,\[ f(t) = 4t^{3/2} - 5t + C_2. \]
04
Use Initial Condition on Function
We use the initial condition \( f(4) = 20 \) to find \( C_2 \):\[ f(4) = 4(4)^{3/2} - 5(4) + C_2 = 20. \]Calculating \( 4 \times 8 - 20 + C_2 = 20 \), we simplify to \( 32 - 20 + C_2 = 20 \).Solving for \( C_2 \), \( C_2 = 8 \). Thus, \( f(t) = 4t^{3/2} - 5t + 8 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Antiderivatives
In calculus, finding the antiderivative is like doing a reverse operation of differentiation. When you're given a function, like the second derivative of a function, you're tasked with finding its primitive function(s). In the context of our exercise, we start by determining the antiderivative of the second derivative \( f''(t) = \frac{3}{\sqrt{t}} \). To achieve this, we rewrite the function as \( 3t^{-1/2} \) to facilitate simple integration. This rewriting allows us to easily integrate it to find the first derivative \( f'(t) \).
- The antiderivative of \( 3t^{-1/2} \) is found by using the power rule of integration, resulting in \( 6t^{1/2} + C_1 \), where \( C_1 \) is a constant.
- This process continues as we find another antiderivative to reach the function \( f(t) \), starting from \( f'(t) = 6t^{1/2} - 5 \), leading to \( f(t) = 4t^{3/2} - 5t + C_2 \).
Initial Conditions
Initial conditions allow us to pin down a specific solution from the family of solutions given by the antiderivative. When you integrate a function, you arrive at a general solution with unknown constants, like \( C_1 \) and \( C_2 \) in our example. Initial conditions are specific points or values that the function must satisfy, which help immensely in finding these constants.
- Consider \( f'(4) = 7 \), an initial condition that determines \( C_1 \). By substituting \( t = 4 \) in \( f'(t) = 6t^{1/2} + C_1 \), you can solve for \( C_1 \).
- Similarly, the condition \( f(4) = 20 \) allows us to determine \( C_2 \) by substituting \( t = 4 \) in \( f(t) = 4t^{3/2} - 5t + C_2 \).
Constant of Integration
The constant of integration is an integral component when you solve antiderivatives. Each antiderivative operation introduces a constant (like \( C_1 \) and \( C_2 \) in our solution) because integration is essentially 'losing' derivative information, as differentiation reduces dimensional specifics.
- For each integration performed, a constant is added, representing that the antiderivative could be shifted in the vertical or horizontal space.
- For the problem we're working on, these constants are crucial to finding solutions that meet our initial conditions.