Arc Length: Difficulty With The Integral The question is to find the arc length of a portion of a function.
$$y=\frac{3}{2}x^{2/3}\text{ on }[1,8]$$
I couldn't quite figure out how to evaluate the integral, so I appealed to the solution manual for aid.

I don't quite understand what they did in the 5th step. Could someone perhaps elucidate it for me?

The expression in brackets is precisely what you need for the substitution $u=x^{2/3}+1$ to work. 
