In: Math
What are the first five terms of the geometric sequence a1 = 3, an = 4 ⋅ an − 1?
Consider a geometric sequence with recursive formula,
a1 = 3
an = 4 ∙an-1 ...... (1)
First term of given sequence is, a1 = 3
Substitute n = 2 and a1 = 3 in formula (1) an = 4 ∙an-1 and compute second term,
a2 = 4 ∙ a1
= 4 × 3
= 12
Substitute n = 3 and a2 = 12 in formula (1) an = 4∙an-1 and compute third term,
a3 = 4∙a2
= 4 × 12
= 48
Substitute n = 4 and a3 = 48 in formula (1) an = 4∙an-1 and compute fourth term,
a4 = 4∙a3
= 4 × 48
= 192
Substitute n = 5 and a4 = 192 in formula (1) an = 4∙an-1 and compute fifth term,
a5 = 4∙a4
= 4 × 192
= 768
Therefore, first five terms of given sequence is {3, 12, 48, 192, 768}.
Therefore, first five terms of given sequence is {3, 12, 48, 192, 768}.