# Math Help - Geometric sequence help

1. ## Geometric sequence help

Find the tenth term of -1,2,-4,...

how do i find out what r is? do i have to use a1 r^(n-1)?

2. Originally Posted by NeedHelp18
Find the tenth term of -1,2,-4,...

how do i find out what r is? do i have to use a1 r^(n-1)?
$r = \frac{2}{-1} = \frac{-4}{2} = -2$.

3. ok so r = -2

im lost as to how do u find r...

4. Originally Posted by NeedHelp18
ok so r = -2

im lost as to how do u find r...
Go back and read my post - I have showed you how. It's the common ratio.