[justify]Given four distinct points A, B, C and D of the same plane, neither three points are collinear ones. If segments AB, BC, CD and AD intersect only at the ends, the joining of these segments is a quadrilateral. A quadrilateral is also called a four-sided polygon, with four angles. [/justify]
Move points A, B, C or D. Will these four points always determine a quadrilateral?[br]
[justify]Check the "Show / Hide internal angles" box. Move the vertices and observe what happens with the angles and the quadrilateral. Write another definition for convex and concave quadrilaterals.[/justify]
Check the option "Show / Hide diagonal" and demonstrate why the sum is always 360º.[br]
Check the "Show / Hide diagonal" option and explain why the sum is always equal to 360º.