Question

For the following geometric sequence find the explicit formula: {-1, 3, -9,...}

Answer 1

multiplies by -3 every time

Answer 2

`a_(n)` = - 1
`(-3)^(n-1)`

Explanation:

The explicit formula for a geometric sequence is

`a_(n)` = a
`(r)^(n-1)`

where a is the first term and r the common ratio

Here a = - 1 and r = 3 ÷ - 1 = - 3 , thus explicit formula is

`a_(n)` = - 1
`(-3)^(n-1)`