For the following differential equations:
a) Find the characteristic equation of each differential equation and solve
b) Find the general solution of each differential equation.
y⁽⁴⁾−4y⁽³⁾ + 8y⁽²⁾-8y⁽¹⁾ + 4y = 4eˣ(x² sen 3x + 2x cos²x - 3xe²ˣ )