Use method of undetermined coefficients to find a particular
solution of the differential equation ?′′ + 9? = cos3? + 2. Check
that the obtained particular solution satisfies the differential
equation.
Use the method of Undetermined Coefficients to find a general
solution of this system X=(x,y)^T
Show the details of your work:
x' = 6 y + 9 t
y' = -6 x + 5
Note answer is: x=A cos 4t + B sin 4t +75/36; y=B cos
6t - A sin 6t -15/6 t