Question

Write the explicit formula for the geometric sequence.

a1 = -5 a2 = 20 a3 = -80

A. an = -5 • (-4)n

B. an = -5(-4)n-1

C. an = -4(-5)n-1

D. an = -5 • (4)n

Answer 1

Just waiting for some help.........

Answer 2

\(\huge {a _{n} = a _{1}.r^{n-1}}\)

Answer 3

see, \(\huge a _{1} = -5 \)
find \(\huge r\) :))

Answer 4

\(\huge r=\frac{ a _{2} }{ a _{1} }\)

Answer 5

So that would be \[\frac{ 5^{_{2}} }{ 5_{1} }\]

Answer 6

no,
see \(\huge a _{2} = 20 \) :D

Answer 7

So \[\frac{ 20 }{ 10 } then?\]

Answer 8

\(\huge a _{1} = -5 \)

\(\huge r=\frac{ 20 }{ -5 }\)

Answer 9

So we got r, where do I go from there?

Answer 10

\(\huge {a _{n} = a _{1}.r^{n-1}}\)

you will find \(\huge a _{n}\) by your \(\huge r\) :))

Answer 11

I don't know how to solve that.

Answer 12

whats your \(\huge r \) ?

Answer 13

20/-5

Answer 14

Whats the result of it?

Answer 15

i mean 20/-5= ?

Answer 16

-4?

Answer 17

Yes,
then an= -5.(-4)^n-1

Answer 18

Thank you very much

Answer 19

hope you understand :)

Answer 20

an = a1 * r ^ n - 1
r = the difference between each term....what you multiply by to get the next number
a1 = the first number