Arithmetic and Geometric Sequences

• Arithmetic Sequence
  • General Term: Tn = a + (n – 1)d
  • Sum of n terms = (2a+(n-1)d) * n / 2
    或
    Sum of n terms = (1st term + last term)*n / 2
• Geometric Sequence
  • General Term: Tn = aR^(n – 1)
  • Sum of n terms = a (1 - R^n) / (1 - R)
  • If -1 < R < 1, sum to infinity of geometric series = a / (1-R)