How do we use pi?

Question

Say a line is 5cm long and we want to know it's pie what do we do 5cm x 3.141592653589793238462643383279502884197169399375105820974944592 and what? Or is that wrong?

Answer 1

Is your line the diameter or the circumference ?

'pi', the small case Greek letter 'p', is the proportion between the circumference and the diameter of a circle. This has been known since classical(ancient Greece) times. The ancient Greeks realised that the circumference of a circle when divided by the diameter( or 2 radii) always produced the ratio we know as 'pi'. It does/did not matter how big or small the circle was, the same ratio 'pi' was the result.
'pi' is an irrational number, the decimals go to infinity and the order of the decimals is random.
For everyday purposes 'pi' = 3.1416
The two equations to learn are;_

C = 2*pi*r = pi*d
C(Circumference), r(radius), d(diameter)
A = pi*r^2
A(Area), r(radius)

Taking your line of 5cm and assuming it to be the diam meter, then the circumference is ;
C = 3.1416 x 5 = 15.708 (3 dp)

Or taking your 5 cm to be the circumference then the radius is
5 = 2 x 3.1416 x r
r = 5 / (2 x 3.1416) = 0.7958 (4 dp)

and area is
A = 3.1416 x 0.7958^2 = 1.9894 units^2

Hope this helps!!!!!

Answer 2

Pie is used for finding areas and circumferences of circles:
circumference: diamiter * pi
Area: radius * radius * pi

Answer 3

Pi is used to find circumference, area, surface area or volume of circles or spheres.

Circumference = diameter * pi
Area = radius ^2 * pi
Surface area = 4 * pi * radius ^2
Volume = 4 / 3 * pi * radius ^2