1. The problem statement, all variables and given/known data r(t)=<cos(t),sin(t),ln(cos(t))> Find T(t) (and N(t)) at (1,0,0) 2. Relevant equations 3. The attempt at a solution T(t)=(dr/dt)/ldr/dtl dr/dt = <-sin(t),cos(t),-tan(t)> ldr/dtl = (sqrt)((-sin(t))^2+(cos(t))^2+(-tan(t))^2) = sec(t) therefore T(t)= (<-sin(t),cos(t),-tan(t)>)/sec(t) = <-tan(t), 1, -sin(t)/cos^2(t)> The problem I'm having is determining which value for the given point do I use to evaluate T(t) (and thereby N(t) and B(t)). How do I tell which value is best or is there a specific value from the point that is always used? Usually it's easier to tell if one of the values is given in radians, such as pi/2. Thanks for any help you can give me.