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## Homework Statement

Suppose that [itex]\vec r(t)[/itex] is a parameterised curve defined for [itex]a \le t\le b[/itex] and

[itex] \displaystyle s(t)=\int_{a}^{t}\left \| d \vec r (t) \right \|dt[/itex] is the arc length function measured from r(a)

a) Prove that s'(t) = || dr(t)||

How do I start this? It is easy to see that differentiating both sides will yield the proof but I don't know how to go about t. Any clues?

Note I have this also posted at MHF with no replies

http://www.mathhelpforum.com/math-help/f57/parameterised-curve-proof-part-1-a-191196.html"

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