Question

If the n^th term of geometric progression $5 , - \frac { 5 } { 2 } , \frac { 5 } { 4 } , - \frac { 5 } { 8 } , \ldots$ is $\frac { 5 } { 1024 }$, then the value of n is.

• A. 11
• B. 10
• C. 9
• D. 4

Answer 1

Answer: (A)

11

Answer 2

$T _ { n } = a r ^ { n - 1 }$ ⇒

⇒ $\left( \frac { - 1 } { 2 } \right) ^ { 10 } = \left( \frac { - 1 } { 2 } \right) ^ { n - 1 }$⇒ $10 = n - 1$⇒ $n = 11$.