If a, b, c are in G.P. and x, y are the arithmetic means of a, b and b, c respectively,
then prove that and
Let the G.P. be a, ar, ar2, ..........
Given a + ar = -4 ...(i)
Also,
or
(∵ )
Putting r = 2 in (i), we get a + 2a = -4 a = -4/3.
∴ G.P. is
Now, putting r = -2 in (i), we get a + a(-2) = -4 -a = -4 or a = 4.
∴ G.P. is 4, 4(-2), 4(-2)2, .... or 4, -8, 16, ...........