+28 I have a question regarding a solution
The 1st, 4th, and 8th terms of an AP are themselves geometric progression. What is the common ratio of the GP?
where:
1st term = a
4th term = a+3d
8th term = a+7d
The solution given by my teacher is apparently:
(a+3d) ^2 = a (a+7d)
9d^2 = ad
d ( 9d-a) = 0
a = 9d
So numbers in AP are
9d, 12d , 16d
r = 12/9 = 4/3
what formula was (a+3d) ^2 = a (a+7d) from?
