Try this
Adjust the tetragon below by dragging any orange dot. By clicking on the top left command line,
you can switch it between a
regular and
irregular tetragon.

Because a tetragon has an even number of sides, in a
regular tetragon, opposite sides are
parallel. A regular tetragon is a
square.

Properties of regular tetragons

Interior angle

90°

Like any regular polygon, to find the interior angle we use the formula
(180n–360)/n . For a tetragon, n=4.
See Interior Angles of a Polygon

Exterior Angle

90°

To find the exterior angle of a regular tetragon, we use the fact that the exterior angle
forms a
linear pair
with the interior angle, so in general it is given by the formula
180-interior angle.
See Exterior Angles of a Polygon

The number of distinct diagonals possible from all vertices. (In general ½n(n–3) ).
In the figure above, click on "show diagonals" to see them.
See Diagonals of a Polygon

Number of triangles

2

The number of triangles created by drawing the diagonals from a given vertex. (In general n–2).
In the figure above, click on "show triangles" to see them. See Triangles of a Polygon