Question

The 1st and 8th term of a G.P. are 4 and 512 respectively. Find 1. Common ratio 2. Sum of its first 5 terms

Answer 1

the common ratio is 2/3 and the sum of 5 terms is and sum I m not getting sorry..     

Answer 2

Answer:

1. Common Ratio, r=2

2. Sum of 5 term = 124

Step-by-step explanation:

Given : The 1st and the 8th term of a GP are 4 and 512 respectively.

Using GP formula, $a_n=ar^{n-1}$

1. First term, a=4 and $a_8=512$

$4\cdot r^7=512$

$r^7=128=2^7$

            r=2

Thus, Common Ratio, r=2

2. Sum of first 5 term

Formula, $S_n=\dfrac{a(r^n-1)}{r-1}$

Where, a=4, r=2 and n=5

$S_5=\dfrac{4\cdot (2^5-1)}{2-1}$

$S_5=4\times 31$

Thus, Sum of first 5 term of GP is 124