Question

If the area of a circle is 81π square feet, find its circumference. ​

Answer 1

$\mathfrak{\underline{\underline{Question :}}}$

If the area of a circle is 81π square feet, find its circumference. 

$\mathfrak{\underline{\underline{Answer :}}}$

18π feet

$\mathfrak{\underline{\underline{Explanation:}}}$

The area is given by π × r × r.

Hence,

π × r × r = 81π

π gets cancelled

r × r = 81 → r = 9 feet

The circumference is given by ,

2 × π × r = 2 × π × 9 = 18 π feet

Answer 2

Answer :

The circumference is 18π feet.

Step-by-step explanation :

Given that :

The area of a circle is 81 π square feet.

To Find :

The circumference of the circle.

Solution :

First of all we have to find Radius.

Finding Radius :

We know that :

⇒ Area = πr²

As Given :

⇒ Area = 81π ft².

Divide both side by π :

⇒ r² = 81  = √81

Square the both sides :

⇒ r = 9.

Now, To Find its circumference :

We know that :

$\bigstar\;\boxed{\sf Circumference = 2\pi r}}$

Values :

$\tt\\ \implies2\pi (9)\\ \\\implies  18\pi\;feet\\ \\ \\\bigstar\;\textbf{\underline{\underline{Hence,The circumference is 18 pi feet.}}}$