Question

How the perimeter of the circle become $2\pi r$ ?

• A. undefined
• B. undefined
• C. undefined
• D. undefined

Answer 1

Recall that the definition of pi $\left(\pi \right)$ is the circumference c of any circle dividedby its diameter d. Put as an equation, pi is defined as
$\pi =\frac{c}{d}$
Rearranging this to solve for c we get
$c=\pi d$
The diameter of a circle is twice its radius, so substituting 2r for d
$c=2\pi r$