Question

The diameter of a circle is 42cm, find its perimeter. if the perimeter of the circle is doubled,what will be the radius of the new circle. (Take r=22 by 7​

Answer 1

Diameter=42 cm

Radius=42/2

=21 cm

Perimeter (Circumference)=2πr

$2 \times \frac{22}{7} \times 21 \\ \\ 2 \times 22 \times 3 \\ \\ = 132 \: cm$

Perimeter=132 cm

If Perimeter is doubled

=132×2

=264 cm

We know Perimeter=2πr

A/Q

$2 \pi \: r = 264 \\ \\ 2 \times \frac{22}{7} \times r = 264 \\ \\ r = 264 \times \frac{7 }{22 \times 2} \\ \\ r = 7 \times 6 \\ \\ r = 42$

$\boxed{\mathbf{New\:Radius=42\:cm}}$

Answer 2

Thanks for asking this question friend....

Given :-

r = 21cm i.e. d/2 = 42/2

To find :- 1.Its perimeter

2. Radius of new circle if perimeter is doubled.

Solution :-

1.

$perimeter = 2\pi \times r$

》 2 × 22/7 × 21

》 132 cm

2. If its perimeter is doubled then its radius also get doubled as...

P = 2 * pie * r

》 New perimeter = 2 P

》 New perimeter = 2 * 2*pie *r

= 2* pie * 2r

becuase 2* pie remain constant .

Proof by taking this question :-

New perimeter = 2* pie * r

》 264 = 2 * 22/7 * r

》 132 × 7/22 = r

》 r = 42 cm which is twice of orignal radius i.e. 21 × 2

.....Hope it helps you a lot .....