The characteristic equation is obtained by replacing $\frac{d}{dt}$ with $s$ in the differential equation. Therefore, the characteristic equation is $s^2 + 2s + 1 = 0$.

The poles of a system are the values of $s$ that make the denominator of the transfer function equal to zero. In this case, the denominator is $s(s+1)$, so the poles are $s = 0$ and $s = -1$.

The Laplace transform of $e^{-at}$ is $F(s) = \int_0^\infty e^{-st} e^{-at} dt = \int_0^\infty e^{-(s+a)t} dt = \frac{1}{s+a}$.

Stability in control theory refers to the ability of a system to return to its equilibrium state after being subjected to a disturbance. A stable system is one that does not exhibit unbounded oscillations or diverge from its equilibrium point.

The Routh-Hurwitz criterion is a mathematical tool used to determine the stability of linear time-invariant systems. It involves constructing a Routh array from the coefficients of the characteristic equation and analyzing the signs of the elements in the first column. The stability of the system can be determined based on the number of sign changes in the first column.

The transfer function of a linear system in state-space representation is given by $G(s) = C(sI - A)^{-1}B$, where $C$ is the output matrix.

A feedback loop in control theory is used to reduce the system's sensitivity to external disturbances. By feeding back a portion of the system's output to the input, the feedback loop helps to counteract the effects of disturbances and maintain the desired system behavior.

Pole placement, state feedback, and output feedback are all common techniques used to design controllers for linear systems. Pole placement involves selecting the desired locations of the system's poles to achieve the desired system behavior. State feedback utilizes the full state information to design the control law, while output feedback uses only the measured output to design the control law.

The order of a differential equation is the highest order of the derivative that appears in the equation. In this case, the highest order of the derivative is 3, so the order of the differential equation is 3.

To solve this differential equation, we can use the method of separation of variables. Integrating both sides with respect to $x$, we get $y = \int (2x + 1) dx = x^2 + x + C$, where $C$ is the constant of integration.

The Van der Pol equation, Duffing equation, and Logistic equation are all examples of common types of nonlinear differential equations. These equations exhibit nonlinear behavior due to the presence of nonlinear terms, such as quadratic or exponential terms.

The general solution of this differential equation can be obtained by using the method of undetermined coefficients. Assuming a solution of the form $y = A\cos(\omega t) + B\sin(\omega t)$, we can find the values of $A$ and $B$ by substituting this solution into the differential equation.

The Laplace transform of $t^2 e^{-at}$ can be obtained by using the formula $\mathcal{L}{t^n e^{-at}} = \frac{n!}{(s+a)^{n+1}}$. Therefore, $F(s) = \mathcal{L}{t^2 e^{-at}} = \frac{2!}{(s+a)^3} = \frac{2}{(s+a)^3}$.

The integrating factor for a first-order linear differential equation of the form $\frac{dy}{dx} + P(x)y = Q(x)$ is given by $e^{\int P(x) dx}$. In this case, $P(x) = 1$, so the integrating factor is $e^{\int 1 dx} = e^x$.

The method of successive approximations, also known as the Picard iteration method, is a common method for solving nonlinear differential equations. It involves starting with an initial approximation of the solution and then iteratively improving the approximation by substituting it back into the differential equation.