Circles: knowing that all measures of a circle are related through the radius is very helpful for Test Day. In circle problems, we should always mark the radius and write down the relevant formulas. There are only a few formulas to memorize for GRE circle geometry. However, being able to apply these formulas and switch from one to the other will make all the difference on our Test Day performance and timing!

Every circle problem on the GRE comes down to using the radius to find some other measure!

An arc is simply a part of the circumference, and a sector is part of the area of a circle which is formed by two radii, and the arc they intercept. If we know the radius of the circle and the degree measure of the arc or sector, we can calculate the

Length of arc = inscribed angle = area of sector

Circumference 360 degree area of circle

For example: To find the area of the sector with a central angle of 90 degrees, given a circle area of 64 pie, simply multiply by the measure of the central angle over 360 degrees.

64 pie ( 90/360) = 64 pie (1/4) = 16 pie

**Join us next time when we’ll discuss translating words into mathematical expressions on the GRE.**

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