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## anonymous 3 years ago Find the general term an for the geometric sequence a1=-3 and a2=6?

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1. anonymous

$a_{1}=-3 and a_{2}=6$

2. RadEn

use the formula : an = a1 r^(n-1) with a1 is given -3 and to get the ratio(r), defined r = a2/a1 = 6/-3 = -2 therefore, an = a1 * r^(n-1) an = -3 * (-2)^(n-1) |dw:1367598379663:dw|

3. anonymous

so that's the answer? @RadEn I'm confused

4. nincompoop

it is not the answer, rather hint as how to solve the problem.

5. anonymous

ahhh!! i'm so lost and confused!! @nincompoop

6. anonymous

Can you find here the common ratio "r" ??

7. anonymous

-2?

8. anonymous

Yep..

9. anonymous

So, general term can be found as: $\large \color{green}{a_n = a \cdot r^{n-1}}$

10. anonymous

a = -3 and r = -2.. Plug in and find..

11. anonymous

6?

12. anonymous

How?

13. anonymous

Use that formula,

14. anonymous

-3(-2)^n-1?

15. anonymous

Yep, this is the general term you require...

16. anonymous

okay, but I am stuck here. I dont what is the next step

17. anonymous

i get 6^n-1?

18. anonymous

Hey, this is the required answer, you can't solve it further..

19. anonymous

so this cant get be simplified any more?

20. anonymous

No..

21. anonymous

$\large a_n = -3\cdot (-2)^{n-1}$

22. anonymous

okay... how come tho? 6^n-1 looks like an ideal answer to me.

23. anonymous

You cannot multiply $$-3$$ with $$(-2)^{n-1}$$

24. anonymous

ohhhhhhhhhhh!!!!!!!!!! duh!! now i get it! my brain hurts been studing all week.

25. anonymous

It is okay..

26. anonymous

thank you for your time and patience

27. anonymous

You are welcome dear..

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