$\begin {array} {1 1} (1)\;\large\frac{\mu_0i}{4} \bigg[ \large\frac{1}{r_1}-\large\frac{1}{r_2} \bigg] & \quad (2)\;\large\frac{\mu_0i}{4} \bigg[ \large\frac{1}{r_1}+\large\frac{1}{r_2} \bigg] \\ (3)\;\large\frac{\mu_0i}{2} \bigg[ \large\frac{1}{r_1}-\large\frac{1}{r_2} \bigg] & \quad (4)\;\large\frac{\mu_0i}{2} \bigg[ \large\frac{1}{r_1}+\large\frac{1}{r_2} \bigg] \end {array}$