Question

Can someone please explain me this

Answer 1

1st way

To solve this we need to know ratio.

`- (1)/(5) / (1)/(5) = - 1 \\`

Now we can see that odd numbers of geometric sequence are positive and even numbers are negative. 91 - odd number, so it will be positive. If ratio is equal to -1, than 91st number is

`(1)/(5) \\`

2nd way

Firstly, we need to find ratio.

`- (1)/(5) / (1)/(5) = - 1 \\`

Secondly, we need to use this formula

`b_n=b_1 * q^(n-1) \\`

`b_(91)= (1)/(5) * ( - 1)^(91-1) = (1)/(5) \\`