1.

Which term of the progression 18, -12, 8, … is 512/729 ?

Answer»

By using the formula,

Tn = arn-1

a = 18

r = t2/t1 = (-12/18)

= -2/3

Tn = 512/729

n = ?

Tn = arn-1

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 term of the Progression is 512/729



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