Basic facts about circles that will help on the SAT math section::

TIP: It is a good idea to not get the formulas for circumference and area confused as it can result in the wrong answer - which will probably be a choice on the test. Circumference is simply another word for perimeter or distance around something. Circles do not have a perimeter - just a circumference which is figured out with a different formula. 

 

Radius

The radius extends from the center of a circle to the edge of the circle. The radii (multiple form of radius) will be equal for circles. 

 

Diameter

The diameter of a circle extends from one end of a circle to the other end - passing through the center. Likewise, a chord extends from one end of the circle to the other without passing through the center. 

 

Tangent

Tangents are lines that intersect a circle in exactly one spot or point. 

 

Arc

An arc is simply the length of the edge of a circle. It is also a fraction or percentage of the circle's total circumference. 

 

Sector

If a circle was sliced into pieces, a sector is one of the pie pieces. It is a fraction of the total area of a circle. When solving these types of questions, it is a good idea to think of the circle like a pie or a pizza.