Question

In the diagram, the radius of the outer circle is 2x cm and

the radius of the inside circle is 6 cm. The area of the
shaded region is  200π cm.
What is the value of x?
​

Answer 1

Area shaded = Area big circle- Area of small circle;

200 pi= pi•(2x)^2 -pi•6^2;

200pi= pi•4x^2 -pi•36;

200pi=pi•4(x^2 -9) divide both sides by 4pi;

50=x^2 -9; So x=sqrt(59)~7.68cm