This is my first post, so hello forums

. Anyway, I am trying to relearn calculus, took a hiatus for a while, and I am currently taking beginners multi-variable calculus and I hit an example that I do not understand in my book (probably cause my diff/integral calculus could use some boning up

).

This involves Arc Length and Curvature:

r(t) = cos(t)i + sin(t)j + tk from point (1,0,0) to (1,0,2

)

they show that

and then they say "The arc from (1,0,0) to (1,0,2

) is described by the parameter interval

and so [from formula 3], we have...

I do not understand how they got

?

shouldn't it be

?

Thank you for any and all input