Quadrilateral Angle Theorems

Interact with the applet below for a few minutes.   Then, answer the questions that follow.   Be sure to change the locations of the quadrilateral's BIG BLACK VERTICES each time before you drag the slider!!! Note: M1, M2, M3, & M4 serve as midpoints of the sides of this quadrilateral.
Questions: From your observations, what is the sum of the measures of the interior angles of     any quadrilateral?