Question

if radius of a circle is 21 cm, then what will be the circumference and area ​

Answer 1

Given

• Radius ⇒ 21 cm

_________________________________

To Find

• Area of Circle
• Circumference

_________________________________

Solution

Formula to find the Circumference ⇒ 2πr

Here 'r' is the radius.

Circumference of Given Circle

⇒ $\sf 2\times \dfrac{22}{7}\times 21$

⇒ $\sf 2\times \dfrac{22}{7\div 7 }\times 21\div 7$

⇒ $\sf 2\times 22 \times 3$

⇒ $\sf 132 \ cm$

∴ The circumference of the given circle is 132 cm

Formula to find the Area of Circle ⇒ πr²

Here 'r' is the radius.

Area of Given Circle

⇒ $\sf \dfrac{22}{7}\times (21)^{2}$

⇒ $\sf \dfrac{22}{7}\times 441$

⇒ $\sf \dfrac{22}{7\div 7 }\times 441 \div 7$

⇒ $\sf22\times 63$

⇒ $\sf 1386 \ cm^{2}$

∴ The area of the given circle is 1386 cm²

_________________________________

Answer 2

Answer:

Given :-

• A circle whose radius is 21 cm.

To Find :-

• What is the circumference and area.

Formula Used :-

✧ To find circumference of a circle we know that,

${\purple{\boxed{\large{\bold{Circumference\: of\: circle\: =\: 2{\pi}r}}}}}$

✧ To find area of the circle we know that,

${\purple{\boxed{\large{\bold{Area\: of\: circle\: =\: {\pi}{r}^{2}}}}}}$

Solution :-

➤ To find circumference of the circle,

Given :

• Radius = 21 cm

According to the question by using the formula we get,

⇒ $\sf Circumference =\: 2 \times \dfrac{22}{7} \times 21$

⇒ $\sf Circumference =\: 2 \times \dfrac{22}{\cancel{7}} \times {\cancel{21}}$

⇒ $\sf Circumference =\: 2 \times 22 \times 3$

⇒ $\sf Circumference =\: 44 \times 3$

➠ $\sf\bold{\green{Circumference =\: 132\: cm}}$

$\therefore$ The circumference of the circle is 132 cm .

➤ To find area of the circle,

Given :

• Radius = 21 cm

According to the question by using the formula we get,

↦ $\sf Area =\: \dfrac{22}{7} \times {(21)}^{2}$

↦ $\sf Area =\: \dfrac{22}{7} \times 21 \times 21$

↦ $\sf Area =\: \dfrac{22}{7} \times 441$

↦ $\sf Area =\: \dfrac{22}{\cancel{7}} \times {\cancel{441}}$

↦ $\sf Area =\: 22 \times 63$

➦ $\sf\bold{\red{Area =\: 1386 c{m}^{2}}}$

$\therefore$ The area of the circle is 1386 cm² .