Hello, here I am providing you the details of the circles section of the GMAT exam as under:

Circles - GMAT

Contents:
Definitions
Properties of a Circle
Formulas for Circles
Arcs & Sectors
Arcs
Sectors
Inscribed Angle & Central Angle
Inscribed Triangle
Inscribed Circles & Circumscribed Circles
Inscribed Circles
Circumscribed Circles
Types of GMAT Problems

Definitions
Circle - An infinite set of points that are all equidistant from a point called the center.

Circumference - The edge (or boundary) of a circle.
Radius - A line from the center of a circle to the edge of the circle.
Diameter - A line that passes through the center of the circle and has its endpoints at the edge of the circle.
Chord - A line that lies within the circle and connects two points on the edge of the circle.

Central Angle - An angle whose vertex is the center of the circle.
Arc - A portion of the circumference of a circle (i.e., a segment of the edge of a circle).

Sector of a Circle - A slice (or sliver) of the circle enclosed on one side by the edge of the circle and on the other sides by radii.
Center of a Circle - The point in a circle from which all points on the edge of the circle are equidistant.
Circumscribed Circle - A circle that encompasses (or surrounds from the outside) a polygon such that the circle's circumference intersects the vertices of the polygon.

Inscribed Circle - An inscribed circle is a circle that lies inside a figure such that points on the edge of the circle are tangent to the sides of the figure.
Concentric Circles - Circles with the same center point but not necessarily the same radius length.

Formulas for Circles
Area = πr2
Diameter, d = 2r
Circumference = 2πr = πd
Central Angle = 2(Inscribed Angle)
Area of Sector = (x/360)πr2
Length of an Arc = (x/360)
Circumference = (x/360)2πr