2nd term is 81 ---- ar = 81
4th term is 9 ----- ar^3 = 9
divide second equation by the first
r^2 = 9/81 = 1/9
r = ± 1/3
so ar = 81
a(1/3) = 81
a = 243
ii) you have a type, but now that you have a and r, whatever the question should be simple
iii) sum of infinite
=a/(1-r) = 243/(1-1/3)
= 243/(2/3)
= 243(3/2) = 364.5
The second term of a GP is 81 and the fourth term is 9. Find,
(i) the common ratio,
(ii) the sum of the first terms,
(iii) the sum to infinity.
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