Find an

explicit formula for the geometric sequence 120, 60, 30, 15, ...

f (n) = 120 * (1/2) ^n

Step-by-step explanation:

First the first number is 120, so we get y = 120, then 60/120 = 1/2

So we no the r, or constant rate is 1/2.

After that, we can finish our equation by doing

f (n) = 120 * (1/2) ^n

or

y = 120 * (1/2) ^x

120 (0.5) ^x-1

Step-by-step explanation:

If we look at the sequence we can see that the sequence is decreasing by 1/2 of the other or dividing by 2.

120/2 = 60 60/2 = 30 ...

So, we know the multiplier is 1/2 or 0.5

So ...

120 (0.5) ^x-1