Here the first term is a(1) = 48 and the common ratio (r) is 1/2.
Thus, a(n) = a(1)(1/2)^(n-1). Check: does this formula predict correctly that a(2) = 24? a(2) = 48(1/2) = 24. YES.
a(3) = 12
a(4) = 48(1/2)^(4-1) = 48(1/2)^3 = 48/8 = 6
a(5) = 48(1/2)^5-1) = 48/16 = 3
