There is an infinite wire grid with cells in the form of equilateral triangles. The resistance of each wire between neighbouring joint connections is R₀. The net resistance of the whole grid between the points A and B as shown is

$\frac{R_0}{3}$

By principle of symmetry and superposition,

$2 \times \frac{I}{6} \times R_0=IR_{\text {eq.}} \Rightarrow R_{\text {eq. }}=\frac{R_0}{3}$

(Current $\frac{I}{6}$ in AB is due to division in current entering at A and current $\frac{I}{6}$ is due to current returning from infinity of grid).