well, it's clear that
(m-3)^3 = m^3 - 9m^2 + 27m - 27
now just proceed as usual to solve this type of equation.
consider the differential equation
d^3x/dt^3 - 9(d^2x/dt^2)+ 27(dx/dt) -27x = c0s t +sin t + te^(3t)
a) show that characteristic equation of the differential equation is
(m-3)^3 =0
(b) Hence, find the general solution of the equation.
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