$\begin {array} {1 1} (a)\;\large\frac{\ell i^2}{\pi} & \quad (b)\;\large\frac{\ell i^2}{4\pi} \\ (c)\;\large\frac{\ell^2 i}{\pi} & \quad (d)\;\large\frac{\ell^2 i}{4\pi} \end {array}$
