Question

write the explicit formula for the geometric sequence.
a1= -5 a2= 20 a3= -80

Answer 1

The ratio between each term of the sequence is -4, and the first term is -5. So then its just a matter of plugging in those values for the general formula for a geometric sequence:
\[a _{n}=a _{1}r^{(n-1)}\]
\[a _{n}=-5(-4)^{(n-1)}\]
You will see that this works for a1, a2 and a3 you provided above.

Answer 2

You lost me ): @DeoxNA

Answer 3

oh wait I just didn't read that right... my bad haha (: thank you!

Answer 4

No problem!