Question

Question #e5881

Answer 1

See explanation..

Explanation:

Remember that `pi` is the ratio between the diameter and the circumference of the circle.

If diameter is `1,ci` `rcumference=pi`
If `2,ci` `rcumference=2pi`

So,circumference of circle=`pid` `,d=diameter`

`r=radius=d/2`
So,`d=2r`

So,circumference of circle=`2rpi,or,2pir`

This is a simple poof that i think is the best

Answer 2

here is how you do it friend,

Explanation:

for this, we will need closed line integration.
suppose the radius of a circle is r
and after `dt` time it makes `d theta` angle in the center of the circle having the arc of `dS`
so,
`dS=rd theta`
now,
`S=oint_0^(s)dS`

`=oint_0^(2pi)rd theta`

`=roint_0^(2pi)d theta`

`=r[theta]_0^(2pi)`

`=r[2pi-0]`

`=r2pi`

`=2pir`