Question

Q 35 The radius of a circle is 7 cm. Determine
the radius of another circle whose area is
9 times of the first circle.
Ops: A
21 v 2 cm
B.
16 2 cm
C.
16 cm
D.
21 cm​

Answer 1

Answer:

D

Step-by-step explanation:

area of circle = πr² [r = 7cm]

area of bigger circle = πR² = 9(πr²) (given)

let the radius of bigger circle be R

9(π x 7²) = πR²

π x 49 = πR² / 9

$r = \sqrt{49 \times 9}$

R = √441

R= 21

Answer 2

SOLUTION :-

Area of circle = $\sf \pi {r}^{2} [r = 7cm]$

⇒ Let the radius of bigger circle be R.

Area of bigger circle = $\sf \: π{R}^{2} = 9(π {r}^{2} ) [given]$

$9(\pi \times {7}^{2} ) = \pi {R}^{2}$

$\sf \pi \times 49 = \frac{\pi {R}^{2}}{9}$

$R = \sqrt{49 \times 9}$

$R = \sqrt{441}$

$\fbox{R = 21cm}$

OPTION D is correct answer.