I need to do a laplace transform on cos^3 t. I understand laplace but the trig is tripping me up. cos^3 t = Cos^2 t * Cos t = cos t * (cos 2t + 1)/2 (double angle formula) so i have (cos t)*(cos 2t)/2 + (cos t)/2. my book's solution says (cos t)*(cos 2t)/2 = (1/2)(cos (2t+1) + cost (2t-1))... how? I cant think of any formulas that give the above result. can someone please explain? thanks.