Question

If the third term is 20 and 7th is 1.25, find the 11th term

Answer 1

the 11th term is 0.0000488 or 4.88*10^-5.

Explanation:

a3 = 20, a7 = 1.25

a7 = a3r^7-3

1.25 = 20r^4

r^4 = 0.0625

r = 4th root of 0.0625

r = 0.5

a3 = a1r^3-1

20 = a1(20)^2

400a1 = 20

a1 = 0.05

a11 = 0.05(0.5)^11-1 = 0.0000488 or 4.88*10^-5