Answer:
see below
Step-by-step explanation:
The formula for a geometric sequence is
an = a1 * r^ (n-1) where a1 is the first term and r is the common ratio
The common ratio is found by taking the second term and dividing it by the first term
a) 1, 2,4.........
a1 = 1
r = 2/1 = 2
an = 1 * ( 2) ^ (n-1)
Let n = 4
a4 = 1 * 2^ (4-1) = 1 * 2^3 = 8
b)50, 20, 8.........
a1 = 50
r = 50/20= 5/2
an = 50 * ( 5/2) ^ (n-1)
Let n = 4
a4 = 50 * (5/2)^ (4-1) = 50 * (5/2)^3 = 3125/4
