There are several formulas for circles. One of the most important formulas
is the formula for the circumference. To find the circumference, you
multiply the diameter, which is double the radius, by the number Pi. Pi is a
transcendental number, which is an irrational number that is not algebraic.
However, Pi can be shortened to 3.1415926535 or simply 3.14. Some
people replace Pi with 22/7, which is very close in value. You can find a
program to calculate Pi and other transcendental constants here.
To find the area of a circle, you square the radius and multiply that by the
number Pi. Circles are generally easier to work with.
To calculate data for sectors, divide the number of degrees by 360 and
multiply that with the circumference or area, whichever you are calculating.
You can find more information here.
Formulas for Polygons:
Polygons have many things that can be calculated. You can find all the
formulas here.
Squares, Cubes, and Rectangular Prisms:
These objects are really simple. To find the area of a square, just square the
sides. To find the perimeter, just multiply a side by four. For cubes, the
formulas are slightly more complex. To find the volume, take the length of
one of the sides and cube it. (example: length is 5 cm long; volume would
be 125 cubic cm.)
Find out more information here.
3-Dimensional Objects:
You can find the formulas here.