Let a be the first term and r be the common ratio of the G.P.
∴ a = –3
It is known that, an = arn–1
∴ a4 = ar3 = (–3) r3
a2 = a r1 = (–3) r
According to the given condition,
(–3) r3 = [(–3) r]2
⇒ –3r3 = 9 r2 ⇒ r = –3 a7 = a r 7–1 = a
r6 = (–3) (–3)6 = – (3)7 = –2187
Thus, the seventh term of the G.P. is –2187.
