### Theory:

All circles are similar to one another. So, the ratio of the circumference to that of diameter is a constant,

That is $\frac{\mathrm{Circumference}}{\mathrm{Diameter}}=\mathrm{constant}$(pi$\mathrm{\pi }$)

Therefore $\frac{C}{d}=\pi$ (Where the approximate value of $$π$$ is $$3.14$$)

$$C$$$$=$$  $d·\pi$  or $$C$$$$=$$ $d·3.14$

The diameter is twice the radius ($$2r$$), so the above equation can be
written as $C=2r·\pi$ Note: $$d$$$$=$$$$2r$$
Therefore, the circumference of a circle, $$C = 2$$$\mathrm{\pi }$$$r$$ units.