### Home > CC2MN > Chapter cc29 > Lesson cc29.1.2 > Problem 9-31

9-31.

The circle shown at right has a diameter of 20 cm. Homework Help ✎

What measurement do you need to find in order to calculate the area inside the circle?

Find the area inside the circle using the formula

*A*=*r*^{2}*π*. Write your answer as a product of*r*^{2}and*π*, and as an approximation using*π*= 3.14.

Recall the equation for area from the Math Notes box in this lesson.

A = *r*^{2} π

What measurement is missing in this equation?

Diameter = 2 (radius)

Solve for *r*.

Substitute the newly calculated radius into the area formula.

20 = 2 *r*

*A* = (10)^{2} π

314 cm^{2}