# Homework Help: Length of spiral

1. Sep 26, 2004

### Monsu

a spiral given by r(t) = (e^-t cos t, e^-t sin t) , t is greater than or equal to 0, how would i find the length of the spiral?
thanks anyone!

2. Sep 26, 2004

### vsage

do a line integral. length = S(dr) from t = 0 on out to infinity in this case. dr is sqrt(dx^2+dy^2) (assuming this is two and not three dimensions) where dx is the derivative of the i component of r(t) and dy is the derivative of the j component of r(t). Oh sorry S also means integral in my bastardized way of writing math with basic text.

Last edited by a moderator: Sep 26, 2004