Question

What is the difference between radius & diameter ?

Answer 1

Diameter is the ratio of the circumference of the circle to the circle to the irrational constant 'pi' $\left(\mathrm{3.1415..}\right)$. Radius is the half of the diameter.

$D=2\times$ radius and radius $=\frac{D}{2}$

Actually pi is defined to be the ratio of the circumference of the circle to the diameter of the circle. Therefore, you can solve for the diameter from that equation.

$\pi =\frac{C}{D}$, or $D=\frac{C}{\pi }$ or $C=\pi \times D$