Hi people, as you can see i am new in this forum. Sorry if i am posting in wrong section. Im going to try to traduce the problem. " f(n) is the sum o n terms of a arithmetic progression. " Show that : f(n+3) -3f(n+2) + 3f(n+1)-f(n) = 0 I just want to know if -3f(n+2) = f(-3n -6) ??