Question

The area difference of the two concentric circles is 770 cm and the radius of their radius is 7 cm, find the radius of both circles.​

Answer 1

Answer:

the radius of both circles are 14 cm and 21 cm.

Step-by-step explanation:

since it is a concentric circle

then there are 2 circles. one is small and one is bigger than the small.

let the radius of the small circle is R cm.

then the radius of the big circle is (R+7) cm.

the area of the small circle is pi*R^2 cm^2

and the area of the big circle is pi*(R+7)^2 cm^2

the diffrence between two circles are 770 cm^2

so, the equation is

pi*(R+7)^2-pi*R^2=770

=>(R+7)^2-R^2=770/pi

=>R^2+24R+49-R^2=245

=>24R=196

=>R=14

so the radius of the small circle is 14cm.

the radius of the big circle is (14+7)cm.

                                                =21cm.