Respuesta :

Solution

For this case we have the following sequence:

-9, -15, -21, -27

Then we can find the common difference on this:

d= -15-(-9)= -15+9= -6

d= -21-(-15)= -21+15= -6

Then the general formula would be given by:

d. an = -9 +(n-1)*(-6)

then the correct solution for this case is:

d.