(d) π : 3.
Let each side of the equilateral Δ be a units.
Then, circumradius of the circle = \(\frac{\text{side}}{\sqrt3}\) = \(\frac{a}{\sqrt3}\) units
∴ Area of circumcircle = \(\pi\bigg(\frac{a}{\sqrt3}\bigg)^2\) = \(\frac{\pi{a}^2}{3}\) sq units
Area of square of side a units = a2 sq units
∴ Required ratio = \(\frac{\frac{\pi{a}^2}{3}}{a^2}\) = \(\frac{\pi}{3}\) = π : 3.