## anonymous one year ago Given the sequence -1, 2, -4, 8, ..., identify the tenth term. Show your work.

1. AlexandervonHumboldt2

look: 2/-1=-2 -4/2=-2 8/-4=-2 any ideas?

2. AlexandervonHumboldt2

so the common ratio is -2

3. anonymous

But what formula will help me find the 10th ?

4. AlexandervonHumboldt2

To find any term of an arithmetic sequence: $a _{n}=a _{1}+\left( n-1 \right)*d$ where $a _{1}$ is the first term of the sequence, d is the common difference, n is the number of the term to find.

5. idku

this is a geometric series, alexnader

6. idku

you are incorrect

7. AlexandervonHumboldt2

woops thx @idku let me give another formula

8. AlexandervonHumboldt2

To find any term of a geometric sequence: where $a _{1}$ is the first term of the sequence, r is the common ratio, n is the number of the term to find. $a _{n}=a _{1}*r^\left( n-1 \right)$

9. AlexandervonHumboldt2

thx @idku for correcting me.