Three semi- infinite rods uniformly charged out of which one is negatively charged and other two are positively charged are kept perpendicular to plane of paper outward such that the finite ends of the rods are located at points A, B and C on a circle of radius R as shown in figure. The net electric field at centre of circle O is :

The system will be superposition of fields due to 3 different wires, the fields in the planes with a magnitude of $\frac{\mathrm{K\lambda }}{\mathrm{R}}$ will be along BO, AO and OC. Resulting in a field of  along OC

And the field due to wires at A and B will be into the plane and field due to the wire at C will be out of the plane resulting in a field of $\frac{\mathrm{K\lambda }}{\mathrm{R}}$
Thus net electric field at point O is given as
${\mathrm{E}}_{\mathrm{net}}=\frac{\mathrm{K\lambda }}{\mathrm{R}}\sqrt{5}$
Resulting electric field at O is at an angle  $\mathrm{\theta }$ from OC where we have
$\mathrm{tan\theta }=\frac{\mathrm{K\lambda }/\mathrm{R}}{2\mathrm{K\lambda }/\mathrm{R}}=\frac{1}{2}$