If vector r(t) is not 0, show that d/dt |r(t)| = (1/|r(t)|) r(t)dot r'(t).
The hint given was that |r(t)|^2 = r(t) dot r(t)
The Attempt at a Solution
the post I saw about this question said that you should take the derivatives of both sides of the hint equation using chain rule, so I got:
2|r(t)|(1)=r'(t) dot r(t) + r(t) dot r'(t)
which is equal to:
|r(t)|= r'(t) dot r(t)
aaaaand now I don't know what to do