variable "d" usually stands for diameter
If given radius "r"
2*r= d
The circumference of a circle is
[tex]C= 2 \pi r= \pi d[/tex]
hence if given circumference
[tex]d= \frac{C}{\pi} [/tex]
The area of a circle is
[tex]A= \pi r^2 = \frac{\pi}{4} d^2[/tex]
hence if given area
[tex]d= \sqrt{\frac{4A}{\pi}}[/tex]
