Find the function \( F \) that satisfies the following differential equations and initial conditions. \( F^{\prime \prime}(x)=\cos x, F^{\prime}(0)=9, F(\pi)=9 \) \( F(x)=\square \) (Type an exact answer in terms of \( \pi \).)
Real Tutor Solution
Answer
Solution
Reviewed and approved by the UpStudy tutoring team
The Deep Dive
To solve for the function \( F(x) \) that satisfies \( F^{\prime \prime}(x) = \cos x \), we start by integrating \( F^{\prime \prime}(x) \). 1. First, integrate \( F^{\prime \prime}(x) \): \[ F^{\prime}(x) = \int \cos x \, dx = \sin x + C_1 \] where \( C_1 \) is a constant to be determined. 2. Next, we use the initial condition \( F^{\prime}(0) = 9 \) to find \( C_1 \): \[ F^{\prime}(0) = \sin(0) + C_1 = 0 + C_1 = C_1 \] Thus, \( C_1 = 9 \). Therefore, we have: \[ F^{\prime}(x) = \sin x + 9 \] 3. Now, integrate \( F^{\prime}(x) \): \[ F(x) = \int (\sin x + 9) \, dx = -\cos x + 9x + C_2 \] where \( C_2 \) is another constant to be determined. 4. We use the next condition \( F(\pi) = 9 \) to find \( C_2 \): \[ F(\pi) = -\cos(\pi) + 9\pi + C_2 = -(-1) + 9\pi + C_2 = 1 + 9\pi + C_2 \] We set this equal to 9: \[ 1 + 9\pi + C_2 = 9 \] Solving for \( C_2 \): \[ C_2 = 9 - 1 - 9\pi = 8 - 9\pi \] 5. Finally, substituting \( C_2 \) back into \( F(x) \): \[ F(x) = -\cos x + 9x + (8 - 9\pi) \] Combining the constants gives the final function: \[ F(x) = -\cos x + 9x + 8 - 9\pi \] Thus, the function \( F(x) \) is: \[ \boxed{-\cos x + 9x + 8 - 9\pi} \]