Question

If a4=16 and a8=32 and an= 128 for an arithmetic sequence what is the value of n?

Answer 1

n = 32

Explanation:

an = a1 + (n - 1)d

a4 = a1 + 3d = 16

a8 = a1 + 7d = 32

7d - 3d = 32 - 16

4d = 16

d = 4

a4 = a1 + 3d = 16

a1 + 3(4) = 16

a1 + 12 = 16

a1 = 4

an = 4 + (n - 1)4 = 128

4 + 4n - 4 = 128

4n = 128

n = 32