I've been given this formula to simplify:
nth term = a (n-1) d + 1/2 (n-1)(n-2)c
I've roped all my friends into helping me with this...! Yet my teacher has looked over them and declared all their attempts as incorrect!
He hints that :
1/2(n squared - 3n+2)c
(but doesn't this actually make the formula more complicated?)
could anybody please help me?
thank you so much