Find the derivative of f (x) = - 9/x at x = 6

F (x) = - 9/x which is equal to:

f (x) = - 9x^ (-1) So the power rule for differentiation is used ...

Power rule: f (x) = x^e, df/dx=ex^ (e-1) so:

df/dx=-9 (-1) x^ (-1-1)

df/dx=9x^ (-2) or if you prefer ...

df/dx=9/x^2

df/dx (6) = 9/36=1/4