# Line Integrals

1. Mar 3, 2013

### ferret123

1. The problem statement, all variables and given/known data

don't know the line integral latex code but;

$\int$$\underline{r}$$\times$d$\underline{r}$

from (a,0,0) to (a,0,2∏b) on the circular helix $\underline{r}$ = (acos(λ), asin(λ), bλ)

3. The attempt at a solution

Its the multiple use of the position vector r in the question thats confusing me. So far i've tried paramaterising the original integral as (r cross dr/dλ)dλ with dr/dλ being the derivative of the circular helix however I am confused as to whether the r in the integral is the same as the one describing the helix.

Am I on the right track or will i need to use another method?

2. Mar 3, 2013

### CAF123

The r given to you is the parametric representation of the helix. It is easy to check that this is a suitable parametrisation.