The value of \(\int\limits_{\rm{A}}^{\rm{B}} {\left( {\overline {\rm{r}} \,{\rm{ \times }}\,{\rm{d}}\overline {\rm{r}} } \right)} \) from A(a, 0, 0) to B(a, 0, 2π b) along r̅ = (a cos t) î + (a sin t) ĵ + b t k̂ is:
1
πa (bĵ + ak̂)
2
2πa (aĵ + bk̂ + abî)
3
2πa (aĵ + bk̂)
4
2πa (bĵ + ak̂)