What is the area and radius of a circle when the circumference is 18 inches ?

Amanda,

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=∏r^{2}. So inserting 9/∏ for r gives us A=∏(9/∏)^{2}. Then A=∏(81/∏^{2}). Simplifying gives A=81/∏, or approximately 25.78 inches.