(Q5).For each geometric progression find the common ratio ‘r’, and then find a
n
.
(ii) 2, -6, 18, -54, ......
Given G.P. = 2, -6, 18, -54, …….
a =
, r =
a
2
a
1
=
-
= -
a
n
= a.r
n-1
=
× (-
)
n-1
∴ r = -
; a
n
=
(-
)
n-1
Clear