How do you get circumfence of a circle?

Answer 1

Remember the two equations, and commit to memory.

C = pi d

C = 2 pi r

Where

pi = 3.141592....

d = 2r = diameter or the sum of two radii.

NB These equations have been known from ancient times. It was noticed that a donkey tethered to a central pole to lift water, went round in a circle, the circle was bigger for a longer tether (radius) .

It was found that the circumference 'C' was always directly proportional to the diamter (d) .

Mathematically

C directly proportional d.

Hence

C = d X a constant(k)

C = d*k

C/d = k 'k' was found to be 3.141592.... for any sized circle , and hence given the name 'pi'. 'pi' is the small/lower case Classical Greek letter 'p'; it means proportion.

Notice how the number '2'

Hence today we use :-

C = pi*d or

C = 2pir

As an additional fact

A(area) = pi r^(2)

Notice how the '2' moves from being an coefficient in 'C' to being a power/exponent in 'A'. The rest remain unchanged.

Hope that helps!!!!!

Answer 2

Diameter times Pi or 3.14= Circumfrence