## Tabbiejack 2 years ago Write the recursive formula for the geometric sequence. a1 = -2 a2 = 8 a3 = -32 A. an = -4 + an-1 B. an = -2 + an-1 C. an = -2 • an-1 D. an = -4 • an-1

1. Tabbiejack

@Hero

2. Tabbiejack

@jim_thompson5910

3. campbell_st

well a term in a geometric series is $a_{n} = a_{1} r^{n -1}$ you have the 1st term -2 you need to find the common ratio r... is can be done by comparing terms $\frac{a_{2}}{a_{1}} = \frac{a_{3}}{a_{2}}$ hope this helps

4. Tabbiejack

I am a parent trying to help my child and I don't understand this.... she has the answer but I don't know if its right

5. campbell_st

6. Tabbiejack

c

7. campbell_st

each term is being multiplied by -4 so term 2 = -4 x term 1 8 = -4 x -2 if its correct try it with term 3 term 3 = -4 x term 2 -32 = -4 x 8 is it correct.. hope this helps...

8. Tabbiejack

so is C right?

9. mahdi2020

$(-1)^{n} * (2)^{2n-1}$ is useful? i can solve 99 percent of math questions

10. Hero

99% are you sure @mahdi2020?

11. mahdi2020

yes sure i`m a engeenier

12. Tabbiejack

ok but I don't understand what is the right answer?

13. Tabbiejack