Help please?

9.8

Step-by-step explanation:

a geometric sequence means we multiply the previous element by a certain factor to get the next element.

so, all we need to do is determine the factor used to go from one element in the list to the next.

a1 = 9

a2 = 88.2

a3 = 864.36

a4 = 8470.728

the simplest case is usually the case from a1 to a2.

a2 = a1×f

88.2 = 9×f

f = 88.2/9 = 9.8

we are finished here.

but we can control our result and verify with the other given elements.

88.2 × 9.8 = 864.36

and that is a3. fits.

864.36 × 9.8 = 8470.728

and that is a4.

so, all fits, we are correct.

the common ratio is 9.8

just divide the term with it's previous term

eg. 88.2/9 , 864.36/88.2