The Total solution for NCERT class 6-12
By using the formula,
Tn =arn-1
a = 18
r = t2/t1 =(-12/18)
= -2/3
Tn =512/729
n = ?
512/729 = 18 (-2/3)n-1
29/(729 ×18) = (-2/3)n-1
29/36 ×1/2×32 = (-2/3)n-1
(2/3)8 =(-1)n-1 (2/3)n-1
8 = n – 1
n = 8 + 1
= 9
∴ 9th termof the Progression is 512/729