Question

The sum of the 1st nth term of a geometric series is 127.the sum of the reciprocal is 127/64,if the 1st term is 1.find n and the common ratio

Answer 1

Answer:

Common ratio = 2

n = 7

Step-by-step explanation:

The formula for the sum of the nth term of a Geometric Progression is given as:

Sn = a(1-r^n)/(1-r)

Where n = Number of terms

r = Common ratio

The sum of the 1st nth term gp is 127.

Hence:

127 = 1(1-r^n)/(1-r)

The sum of the reciprocal is 127/64

This means the inverse, the formula is given as:

Sn = 1/a(1-r^n)/(1-r)

127/64 = 1(1-1/r^n)/(1-1/r)

= r^(1-n)(1-r^n)/(1-r)

Simplifying we have:

1/64 = r^(1-n)

or,

r^(n-1) = 64

r^(n-1) = 2⁶

Hence:

r = 2

Solving for n

n - 1 = 6

n = 6 + 1

n = 7

Therefore:

Common ratio = 2

n = 7