Answer:
y(t) = c_1e^(6t) + c_2e^(-6t) - 2t^2 + 3t,
Explanation:
To find the general solution of the given differential equation, we can first solve the associated homogeneous equation, and then find a particular solution for the non-homogeneous equation. Let's proceed with the steps:
Step 1: Solve the associated homogeneous equation:
The associated homogeneous equation is obtained by setting the right-hand side of the differential equation to zero:
y" - 36y = 0
The characteristic equation for this homogeneous equation is:
r^2 - 36 = 0
Solving the characteristic equation, we get the roots:
r = ±6
Therefore, the homogeneous solution is given by:
y_h(t) = c_1e^(6t) + c_2e^(-6t)
Step 2: Find a particular solution for the non-homogeneous equation:
We can use the method of undetermined coefficients to find a particular solution for the non-homogeneous equation. Since the right-hand side of the equation is a polynomial, we assume a particular solution of the form:
y_p(t) = At^2 + Bt + C
Now we can substitute this particular solution into the original differential equation and solve for the coefficients A, B, and C.
y_p"(t) - 36y_p(t) = -108t + 72t^2
Differentiating y_p(t) twice:
y_p'(t) = 2At + B
y_p"(t) = 2A
Substituting into the differential equation:
2A - 36(At^2 + Bt + C) = -108t + 72t^2
Simplifying and equating coefficients:
-36A = 72 (coefficient of t^2)
-36B = -108t (coefficient of t)
-36C = 0 (coefficient of the constant term)
Solving these equations, we find:
A = -2
B = 3
C = 0
So the particular solution is:
y_p(t) = -2t^2 + 3t
Step 3: Write the general solution:
The general solution of the non-homogeneous equation is the sum of the homogeneous and particular solutions:
y(t) = y_h(t) + y_p(t)
= c_1e^(6t) + c_2e^(-6t) - 2t^2 + 3t
Therefore, the general solution of the given differential equation is:
y(t) = c_1e^(6t) + c_2e^(-6t) - 2t^2 + 3t,
where c_1 and c_2 are arbitrary constants.