Integrate Derivative 4083F4
1. We are given the derivative of a function: $f'(x) = x^2 \sin(3x)$ and the initial condition $f(0) = 5$. We want to find the original function $f(x)$ on the interval $[-2, 2]$.
2. To find $f(x)$, we need to integrate $f'(x)$:
$$f(x) = \int f'(x) \, dx = \int x^2 \sin(3x) \, dx + C$$
where $C$ is the constant of integration.
3. Use integration by parts to solve $\int x^2 \sin(3x) \, dx$.
Let $u = x^2$, so $du = 2x \, dx$.
Let $dv = \sin(3x) \, dx$, so $v = -\frac{1}{3} \cos(3x)$.
4. Applying integration by parts:
$$\int x^2 \sin(3x) \, dx = -\frac{1}{3} x^2 \cos(3x) + \frac{2}{3} \int x \cos(3x) \, dx$$
5. Now, integrate $\int x \cos(3x) \, dx$ by parts again.
Let $u = x$, so $du = dx$.
Let $dv = \cos(3x) \, dx$, so $v = \frac{1}{3} \sin(3x)$.
6. Applying integration by parts again:
$$\int x \cos(3x) \, dx = \frac{1}{3} x \sin(3x) - \frac{1}{3} \int \sin(3x) \, dx$$
7. Integrate $\int \sin(3x) \, dx$:
$$\int \sin(3x) \, dx = -\frac{1}{3} \cos(3x) + C$$
8. Substitute back:
$$\int x \cos(3x) \, dx = \frac{1}{3} x \sin(3x) + \frac{1}{9} \cos(3x) + C$$
9. Substitute this into step 4:
$$\int x^2 \sin(3x) \, dx = -\frac{1}{3} x^2 \cos(3x) + \frac{2}{3} \left( \frac{1}{3} x \sin(3x) + \frac{1}{9} \cos(3x) \right) + C$$
10. Simplify:
$$f(x) = -\frac{1}{3} x^2 \cos(3x) + \frac{2}{9} x \sin(3x) + \frac{2}{27} \cos(3x) + C$$
11. Use the initial condition $f(0) = 5$ to find $C$:
$$f(0) = -\frac{1}{3} \cdot 0^2 \cdot \cos(0) + \frac{2}{9} \cdot 0 \cdot \sin(0) + \frac{2}{27} \cos(0) + C = \frac{2}{27} + C = 5$$
12. Solve for $C$:
$$C = 5 - \frac{2}{27} = \frac{135}{27} - \frac{2}{27} = \frac{133}{27}$$
13. Final solution:
$$f(x) = -\frac{1}{3} x^2 \cos(3x) + \frac{2}{9} x \sin(3x) + \frac{2}{27} \cos(3x) + \frac{133}{27}$$
This function satisfies the given derivative and initial condition on $[-2, 2]$.