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

Question

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

anonymous · Answer

@Hero

anonymous · Answer

@jim_thompson5910

campbell_st · Answer

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

anonymous · Answer

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

campbell_st · Answer

what answer does she have..?

anonymous · Answer

c

campbell_st · Answer

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...

anonymous · Answer

so is C right?

anonymous · Answer

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

hero · Answer

99% are you sure @mahdi2020?

anonymous · Answer

yes sure
i`m a engeenier

anonymous · Answer

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

anonymous · Answer

@Hero can you please help me with this answer

anonymous · Answer

you can check the answers
input n=1, 2 3 , ...
my ans is ok