Question

The 2nd term of an exponential sequence is 9 while the 4th term is 81.find the common ratio,the first term and the sum of the first five terms of the sequence

Answer 1

second term: 9

4th term:81

`(3rd \: term)^(2) = 9 * 81`

=729

`√(729) = 27`

3rd term=27

`{9}^(2) = a1x27 \\ 81 = 27a1`

a1=3 the first term

`81 = 3 * {q}^(3)`

`{q}^(3) = 27`

q=3

`s = 3x \frac{1 - {3}^(5) }{1 - 3} = 364.5`