Question

Write the explicit formula for the geometric sequence.

a1 = -5 a2 = 20 a3 = -80

Answer 1

a2/a1=???
a3/a2=???

Answer 2

i dont understand how to do this?

Answer 3

start by answering the 2 questions i gave you

Answer 4

-4

Answer 5

so the sequence is increasing by multiplying -4 to the previous term

this can be represented by
\[(-4)^n\]

Answer 6

what do i need to do next thought?

Answer 7

though*

Answer 8

\[a_n=B(-4)^{n-1}\]
solve for B

Answer 9

-2

Answer 10

where did you get -2 from?

explicit formula
\[a_n=a_1*r^{n-1}\]

Answer 11

i really just dont understand at all im not getting how im supposed to figure out this problem.

Answer 12

r= -4, this you determined

now just substitute in all the information into the explicit formula
\[a_n=a_1*r^{n-1}\]

Answer 13

A geometric sequence progresses term by term by multiplying the previous term by a common ratio (that's the 'r') to get the next term. The 'n' is the number of times you multiplied by that ratio. a_1 is what you start with.
If you want to find the 5th term, e.g., you multiply what you start with by the common ratio 4 times (n=5, so 4=n-1).