Find the derivative of f(x) = negative 9 divided by x at x = -8.

The derivative given in the question is 
f(x) = - 9 /x
When x = -8, then
f(-8) = 9/8
The negative sign on the right hand side gets cancelled out. From the above deduction, it can be easily concluded that the answer is 9/8. I hope that this is the answer that you were looking for and the answer has actually come to your desired help.