I know what to do - its doing it that is the probelm:

v(t) = < 2^(.5) , e^t , -e^(-t) >

so all you do is square each term and then take the square root of that whole thing: (here is what i got)

|v(t)| = [2 + e^(2t) + e^(-2t)]^.5 but from here i cannot simplify further which my book does...I think i need to find a perfect square but cannot see how. any explanation would be great.

Thanks!

edit* the book's answer is: e^(t) + e^(-t)