Area and Circumference are must knows for your study of circles. Keep in mind that the value of pi can be estimated around 3.14 or 22/7 as a fraction. Many students make errors using these formulas because they are weak with the order of operations so if you are having problems double check your understanding of positive and negative numbers and powers.
some key topics that involve circles:
* diameter and radius
* conic sections
* units of measure