- #1

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This is where I get confused.

It can happen that the parameter [tex]t[/tex]is already the arc length measured from some point. In this case, [itex]ds/dt = 1 =|\alpha'(t)|[/tex]. Conversely, if [tex]|\alpha'(t)| = 1[/tex] then [tex]s = \int_{t_0}^t dt = t - t_0.[/tex]

How did they get that it equals 1? I am not sure what they are saying?