1. The problem statement, all variables and given/known data f(t)=tcos(4t) 2. Relevant equations tnf(t)=(-1)n dF(s)/dsn 3. The attempt at a solution I don't understand why this formula is giving me the oppiste sign of the answer. If I apply the formula I get (16-s2)/(s2+16)2 Because n=1 I need to multiply by a negative but this yields the incorrect answer.