Question

Find the area and the circumference of a circle with radius 9 cm. Write your answers in terms of pi, and be sure to include the correct units in your answers.

Answer 1

Circumference: 18π cm

Area: 81π cm²

1) Since the radius is 9 cm then we can write for the Circumference the following:

`\begin{gathered} C=2\cdot\pi\cdot r \\ C=2\cdot\pi\cdot(9) \\ C=18\pi \end{gathered}`

2) The area is found using another formula:

`\begin{gathered} C=\pi\cdot r^2 \\ C=\pi\cdot9^2 \\ C=81\pi \end{gathered}`

3) Hence, the answers are:

Circumference: 18π cm

Area: 81π cm²