**Sum of the interior angles of a polygon**

The sum of the interior angles of a polygon is

180 ( n — 2 ) °

where n is the number of sides the polygon has.

**Sum of the exterior angles of a polygon**

The sum of the exterior angles of a polygon is 360°.

For a regular polygon that has n sides, each exterior angle is

360°/ n

**Angles in opposite segments of a cyclic quadrilateral**

The opposite angles of a cyclic quadrilateral are supplementary, i.e. 180°.

a + b = 180°

c + d = 180°

**Exterior angle in a cyclic quadrilateral**

The exterior angle of a cyclic quadrilateral is equal to the interior opposite angle.

<B = <D

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