Question

The fourth, seventh and the last term of a G.P. are

10, 80 and 2560 respectively. Find the first term

and the number of terms in the G.P.​

Answer 1

Answer:

Step-by-step explanation:

General term =ar  

n−1

 

where, n=nth term

            r=common ratio

            a=first term

Now, ar  

3

=10..............(1).

ar  

6

=80............(2)

ar  

n−1

=2560.................(3)

Dividing (2) by (1)

r  

3

=8⇒r=2

in (1)

a×8=10⇒a=  

8

10

​  

 

in (3)

8

10

​  

×2  

n−1

=2560⇒2  

n−1

=256⇒2  

n−1

=2  

8

⇒n−1=8⇒n=9