Asked by Gustav

The third, fifth and seventeenth terms of an arithmetic progression are in geometric progression. Find the common ratio of the geometric progression.

Answers

Answered by Steve
We can without loss of generality assume a=1, so

(1+4d)/(1+2d) = (1+16d)/(1+4d)
d = -5/8

The AP is 1, 3/8, -2/8, -7/8, -12/8, -17/8, -22/8, ... -9

The GP is 1, -5/8, 25/64, ...

(-12/8)/(-2/8) = 6
(-9)/(-12/8) = 6
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