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dtl42
Mar25-08, 11:34 AM
1. The problem statement, all variables and given/known data
Find the length of the spiral of r=1/theta for theta\geq2 \pi


2. Relevant equations
\int\sqrt{r^{2}+r'^{2}}


3. The attempt at a solution
I thought of the formula for polar arc length, which is the integral of the square root of the sum of the square of r and the square of r'. I tried to evaluate this from 2 \pi to infinity, but could not come up with a definitive answer. I think it might be infinity, but cannot show it legitimately

dynamicsolo
Mar26-08, 06:38 PM
\int\sqrt{r^{2}+r'^{2}} d\theta

You probably aren't getting help because you haven't shown any work. What did you set up as your integrand? Your limits for the improper integral are correct; it really is possible that the integral doesn't converge. (This curve is called a hyperbolic spiral -- see http://mathworld.wolfram.com/HyperbolicSpiral.html .)