Asked by Alia

The third term of a G.P is 9 and the fifth term is 16. Find
a. the 4th term
b. the sum of the first four terms
Answered by mathhelper
just apply the formulas that you know:
term(3) = ar^2 = 9
term(5) = ar^4 = 16
divide them:
r^2 = 16/9
r = ± 4/3

if r = +4/3, then a(16/9) = 9
a = 81/16

if r = - 4/3, then a(16/9) = 9
a = 81/16

your GP is either 81/16, 27/4, 9, 12, 16, ...
or
your GP is 81,16, - 27/4, 9, -12, 16, .....

take it from there, keep in mind there will be 2 sets of answers for the sum
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