Like the interior angles of a triangle, there is a relationship between the angles of quadrilaterals. Use the applet below to explore the relationships between the angles of quadrilaterals in general, and specifically the angles of parallelograms and trapezoids.

a. How many triangles can you break a quadrilateral down into (using the vertices of the quadrilateral as the vertices of the triangles)? Does this work for ANY quadrilateral?
b. Based off the above observation, the interior angles of a quadrilateral will always add up to how many degrees?
c. What relationships do you observe between the angles of a parallelogram? Why is this true? (Use the properties of parallel lines to defend your argument)
d. What relationships do you observe between the angles of an isosceles trapezoid? Why is this true? (Use the properties of parallel lines to defend your argument)