If 2nd, 3rd and 6th terms of an AP are the three consecutive terms of a GP then find the common ratio of the GP.

We have been given that 2nd, 3rd and 6th terms of an AP are the three consecutive terms of a GP.


Let the three consecutive terms of the G.P. be a,ar,ar2.


Where a is the first consecutive term and r is the common ratio.


2nd, 3rd terms of the A.P. are a and ar respectively as per the question.


The common difference of the A.P. = ar - a


And the sixth term of the A.P. = ar2


Since the second term is a and the sixth term is ar2(In A.P.)


We use the formula:t = a + (n - 1)d


ar2 = a + 4(ar - a)…(the difference between 2nd and 6th term is 4(ar - a))


ar2 = a + 4ar - 4a


ar2 + 3a - 4ar = 0


a(r2 - 4r + 3) = 0


a(r - 1)(r - 3) = 0


Here, we have 3 possible options:


1)a = 0 which is not expected because all the terms of A.P. and G.P. will be 0.


2)r = 1,which is also not expected because all th terms would be equal to first term.


3)r = 3,which is the required answer.


Ans:common ratio = 3


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