Laplace Differential 971Ed4
1. **Problem Statement:**
Solve the differential equation $$y' - 2y = \sin(3t)$$ using Laplace transforms.
2. **Formula and Rules:**
The Laplace transform of a derivative is $$\mathcal{L}\{y'\} = sY(s) - y(0)$$ where $$Y(s)$$ is the Laplace transform of $$y(t)$$.
The Laplace transform of $$\sin(at)$$ is $$\frac{a}{s^2 + a^2}$$.
3. **Apply Laplace transform to both sides:**
$$\mathcal{L}\{y' - 2y\} = \mathcal{L}\{\sin(3t)\}$$
$$sY(s) - y(0) - 2Y(s) = \frac{3}{s^2 + 9}$$
4. **Rearrange to solve for $$Y(s)$$:**
$$Y(s)(s - 2) = \frac{3}{s^2 + 9} + y(0)$$
$$Y(s) = \frac{3}{(s - 2)(s^2 + 9)} + \frac{y(0)}{s - 2}$$
5. **Inverse Laplace transform:**
Use partial fraction decomposition and known inverse transforms to find $$y(t)$$.
6. **Final solution:**
$$y(t) = y(0)e^{2t} + \int_0^t e^{2(t-\tau)} \sin(3\tau) d\tau$$ which can be evaluated further if initial condition $$y(0)$$ is given.
This completes the solution for the first problem.