Question:
The first term of a G.P. is 1. The sum of the third term and fifth term is 90. Find the common ratio of G.P.
Answer:
Let first term of the GP is a and common ratio is r.
3rd term = ar2
5th term = ar4
Now
=> ar2 + ar4 = 90
=> a(r2 + r4 ) = 90
=> r2 + r4 = 90
=> r2 *(r2 + 1) = 90
=> r2 (r2 + 1) = 32 *(32 + +1)
=> r = 3
So the common ratio is 3
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