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## Homework Statement

If vector r(t) is not 0, show that d/dt |r(t)| = (1/|r(t)|) r(t)dot r'(t).

The last part is the dot product of r(t) and r'(t).

## Homework Equations

The hint given was that |r(t)|^2 = r(t) dot r(t)

## The Attempt at a Solution

Not sure where to begin, but I thought that |r(t)| is the length or magnitude of the vector r(t), thus its derivative is zero. If this is correct, then I also need to prove that the right side = zero.