Answer :
It is an arithmetic progression. Note the general rule for AP sequences:
a(n) = a(1) + (n - 1)d
a(1) = 12a (first term)
d = 3a (common difference)
General rule: a(n) = 12a + (n - 1)*3a
a(n) = a(1) + (n - 1)d
a(1) = 12a (first term)
d = 3a (common difference)
General rule: a(n) = 12a + (n - 1)*3a