What is the area and radius of a circle when the circumference is 18 inches ?
The formula for the circumference of a circle is C=2∏r, in which r=radius. To find the radius, then, we insert 18 in for the circumference. So 18=2∏r. Solving for r gives 9/∏, or approximately 2.86 inches.
Now that we have the radius, we can find the area. The formula for the area of a circle is A=∏r2. So inserting 9/∏ for r gives us A=∏(9/∏)2. Then A=∏(81/∏2). Simplifying gives A=81/∏, or approximately 25.78 inches.