What is the formula for the following geometric sequence?

-5, -10, -20, -40,

an = -5 · 2n - 1
an = -5 · (-2)n - 1
an = -2 · (-5)n - 1
an = 2 · (-5)n - 1

A

Step-by-step explanation:

The n th term formula for a geometric sequence is

= a

where a is the first term and r the common ratio

here a = - 5 and r = - 10 ÷ - 5 = 2, thus

= - 5( → A

you didn't post any answer choices, so its not 100% clear what your teacher is looking for

however, log(15/7) is equivalent to log(15) - log(7)

i'm using the rule log(x/y) = log(x) - log(y)