1. The problem statement, all variables and given/known data Quick question. I need to find cos [tex]\vartheta[/tex], where [tex]\vartheta[/tex] is the angle (acute) between two vector-valued functions (which are tangent lines). 2. Relevant equations I think this is relevant: cos[tex]\vartheta[/tex] = (u dot v)/([tex]\left\|[/tex]u|| * [tex]\left\|[/tex]v||) 3. The attempt at a solution Is that the correct equation to use? If so, well, the two equations I'm using both have "t" in them, since they're VVFs. But what do I put in for t? I get the feeling that it's blatantly obvious...Thanks for helping!