a) determine a particular integral of the second order differential equation u'' + Bu' +u = sin(wt)

in the form u(t) = Csin(wt) + Dcos(wt) where C and D are functions of w that should be found explicitly.

b) rewrite u(t) in the form u(t) = Asin(wt + y) where A is the amplitude of the long term response and y is a phase lag between the driving force and the response. show that A = sqrt(C^2 + D^2) and hence that

A = 1/ (sqrt(((1-w^2)^2) + (B^2)(w^2))

Please help!! I'm clueless and desperate