Allow me to make a shameless plug for a very cool project currently underway by my GVSU colleague Matt Boelkins. He is writing a free, open-source calculus textbook that will be available in PDF form ...

Find the principle unit normal vector to the curve given below at the specified point: r(t) = 4cos(t) i + 4 sin(t) j, t=pi/6<BR><BR>I think it's the dot product of something, can't find it in my book.

I didn't care for my other calc books so I won't recommend them.<BR><BR>SvendTofte -- Calculus is generally the branch of mathematics dealing with change (change in functions, change in vectors, ...