Question

The diameter of a circle is $18cm$. What is its

1. Radius
2. Circumference

Answer 1

Given,

Diameter of a circle $D=18cm$

a. As we know that the radius $\left(R\right)$ of a circle is half of its Diameter $\left(D\right)$.

So,

$R=\frac{D}{2}$

$R=\frac{18}{2}$ (Given $D=18cm$)

$R=9cm$

Hence, the radius of the circle is $9cm$.

b. The length of a circle is known as its circumference.

and $Circumference\left(C\right)=\mathrm{\pi }\times \mathrm{Diameter}\left(\mathrm{D}\right)$

Where $\mathrm{\pi }\left(\mathrm{Pi}\right)$ is a mathematical constant with an approximate value $3.14$ or $\frac{22}{7}$

So,

$$\begin{gathered} C=\mathrm{\pi }\times 18 \\ C=3.14\times 18 \\ C=56.52cm \end{gathered}$$

Hence, Circumference of the circle is $56.52cm$.