1. The problem statement, all variables and given/known data If a signal f1[n] begins in a moment N1 and ends in moment N2, and signal f2[n] begins in the moment M1, and ends in the moment M2, derive the formula which states in which moment begins and ends the signal f1[n]*f2[n] 2. Relevant equations 3. The attempt at a solution I haven't got a slightest clue where to begin with this. Can anybody just give me a hint how to derive this? I am trying something with delta functions, but not much luck.