If you draw a multi-sided shape (generally called a polygon) using three or more straight lines, then it has the same number of interior angles as the number of sides.
e.g. a 5 sided polygon (called a pentagon) has five interior angles. if one side is extended slightly at one interior angle, then that extension forms the corresponding exterior angle.
The sum of any interior angle plus its corresponding exterior angle is equal to 180°
In a regular polygon in which all N side lengths and interior angles are identical,
each Exterior Angle (E) is given by
..... E = 360° / N ..... giving 72° for a regular pentagon.
The corresponding interior angle will then be 180° - E which will be 180°-72° = 108°.
There is a general formula for the interior angles ( I ) of an N sided regular polygon which is
..... I = 180° ( N -2 ) / N
-- Best wishes - Majikthise.
An Interior angle is an angle inside a shape. The Exterior angle is the angle between any side of a shape, and a line extended from the next side.