Solve the following DE d?x dt2 + kx = f(t) (i) d?Q dQ (ii) + R dt2 = f(t) dt Hints: Step 1: First, express x, q(t) and f(t) as fourier series under different summation index e.g. I, m on each side Step 2: Combine all the terms on both sides under common E,g,(x) = Emhm(x) Step 3: Ensure same range of l and m, i.e, from 0 o. Then set l = m = k Step 4: Equate the coefficients on both sides