The solution of(x2D2+4xD+2)y = ex is
Question
The solution of(x2D2+4xD+2)y = ex is
Solution
The given equation is a second order linear differential equation with constant coefficients. The general form of such an equation is:
ay'' + by' + c*y = f(x)
where y'' is the second derivative of y with respect to x, y' is the first derivative of y with respect to x, and f(x) is the forcing function. In your case, a = 1, b = 4, c = 2, and f(x) = e^x.
The solution to this type of equation is the sum of the homogeneous solution (the solution to the equation without the forcing function, i.e., ay'' + by' + c*y = 0) and the particular solution (a specific solution to the full equation).
- Solve the homogeneous equation:
The characteristic equation of the homogeneous equation is ar^2 + br + c = 0. In your case, this is r^2 + 4*r + 2 = 0. Solving this quadratic equation for r gives the roots r = -2 ± √2i. Therefore, the homogeneous solution is:
y_h(x) = e^(-2x) * (Acos(√2x) + Bsin(√2x))
where A and B are constants to be determined by boundary conditions.
- Find the particular solution:
A common method for finding the particular solution is the method of undetermined coefficients. However, because the forcing function e^x is a solution to the homogeneous equation, we must multiply it by x to find a solution to the full equation. Therefore, we guess that the particular solution has the form:
y_p(x) = x*(C*e^x)
where C is a constant. Substituting this into the full equation gives:
(x^2D^2 + 4xD + 2)(xCe^x) = e^x
Solving this equation for C gives C = 1/2. Therefore, the particular solution is:
y_p(x) = x*(1/2)*e^x
- Add the homogeneous and particular solutions:
The general solution to the equation is the sum of the homogeneous and particular solutions:
y(x) = y_h(x) + y_p(x) = e^(-2x) * (Acos(√2x) + Bsin(√2x)) + x*(1/2)*e^x
This is the solution to the given differential equation.
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