Write an explicit formula for each sequence Arithmetic sequences : an=a1+d(n-1)
1) 2, 4, 6, 8
2) 15 , 12, 9 , 6
Geometric sequences : gn=g1 *r (n-1 )
3) 5, 10 , 20, 40
4) 1, -2 , 4 , -8

AnsRecursive Formula: an= an-1 + d

Used to find the next term in a sequence using a common difference.

Example: 2, 4, 6, 8, 10

nth term:  1, 2, 3, 4, 5,

a1 = 2        Common Difference is 2

a2 = a2-1 + 2

a2 = a1 +2

a2 = 2 + 2

a2 = 4

Explicit formula: an = an= a1 + d (n-1)

Used to find any term in the sequence depending on the term #.

6, 12, 18, 24, 30, 36, 42, 48, 54...

1,  2,   3,  4,   5,    6,   7,  8,   9,  

Find the term in the sequence if the term number is 28.

a28 = 6 + 6 (28-1)

a28 = 168