Question

If the nth term of a GP is 128 and both the first term a and the common ratio r are 2. Find the number of terms in the GP.

• A. 6
• B. 8
• C. 9
• D. 7

Answer 1

Answer:

D. 7

$a=2,r=2$

$a_n=ar^{(n-1)}$

$128=2\times2^{(n-1)}$

$2^7=2^n$

$n=7$