Question

The radius of a circle is 7 cm . Find the radius of a circle whose area is 4 times the area of the given circle.​

Answer 1

Answer:

The required radius =14cm

Step-by-step explanation:

Given:-

The radius of a circle is 7 cm .

To find:-

Find the radius of a circle whose area is 4 times the area of the given circle.

Using formula:-

Area of a circle whose radius is r units

=πr² sq.units

Solution:-

The radius of the circle(r)=7 cm

Area of the circle=πr²

=>A=(22/7)×7²

=>A=(22×7×7)/7

=>A=22×7

=>A=154 cm²

Area of the circle=154 cm²

Area of the circle whose area is 4 times the given circle=4×154=616cm²

Now we have

πr²=616

=>22/7r²=616

=>r²=616×7/22

=>r²=28×7

=>r²=4×7×7

=>r²=2²×7²

=>r²=(2×7)²

=>r²=14²

=>r=14 cm

Answer:-

The required radius =14cm

Answer 2

Answer:

14 cm

Step-by-step explanation:

Let radius of the two circles be r and R respectively:-

Area of 1st circle = π r²

=(22/7)×7×7

= 22×7

= 154cm²

Area of 2nd circle = π R²

154 × 4 = (22/7)×R²

616 = (22/7) × R²

R² = (616×7) / 22

R² = 196

R = √ 196

R = 14 cm