General Term tn＝t1＋d（n-1)
Arithmetics sum Sn＝n(t1＋tn)/2
General Term tn＝ｔ１×r＾2-1
Geometric sum Sn=t1(1-r＾ｎ)／1－r, r≠0
Infinite Geometric sum S∞＝t1/1-r
I learned these formula.
My Riverside Rapid Digital Portfolio
General Term tn＝t1＋d（n-1)
Arithmetics sum Sn＝n(t1＋tn)/2
General Term tn＝ｔ１×r＾2-1
Geometric sum Sn=t1(1-r＾ｎ)／1－r, r≠0
Infinite Geometric sum S∞＝t1/1-r
I learned these formula.