How do I find the derivative of r = 1/u with respect to time?

[enrion]

I have been given that r = 1/u
and that r(dot) = (-1/u^2) *(du/dt)
How is r(dot) calculated? I don't understand the steps of how to get from r to r(dot)
From my understanding r(dot) should be the derivative of (1/u) with respect to time, but I don't understand how to get to the final answer.

Thank you very much!

 

[fresh_42]

Do you know the chain rule of differentiation? Apply it to $r(t) = (u(t))^{-1}$. Alternatively you can apply the product or Leibniz rule to $1 = r(t) \cdot u(t)$.

 

[enrion]

Do you know the chain rule of differentiation? Apply it to $r(t) = (u(t))^{-1}$. Alternatively you can apply the product or Leibniz rule to $1 = r(t) \cdot u(t)$.

Thank you very much! Clearly I'm having a bad day :(