The first and the third term of a geometric progression are 5 and 80 respectively. What is the 4th term?
2 answers
maybe 20?
no "maybe" in math
given:
a = 5 , ar^2 = 80
then 5r^2 = 80
r^2 = 16
r = ± 4
if r = 4, ar^3 = 5(64) = 320
if r = -4, ar^3 = -320
check:
if r = 4, terms are
5, 20, 80, 320, 1280, ....
if r = -4, terms are
5, -20, 8-, -320, 1280, ...
given:
a = 5 , ar^2 = 80
then 5r^2 = 80
r^2 = 16
r = ± 4
if r = 4, ar^3 = 5(64) = 320
if r = -4, ar^3 = -320
check:
if r = 4, terms are
5, 20, 80, 320, 1280, ....
if r = -4, terms are
5, -20, 8-, -320, 1280, ...