Is the quadrilateral shown here http://static.panoramio.com/photos/medium/89353369.jpg a parallelogram?
In the figure provided, let A, B, C and D represent the vertices starting from the top left and moving in a clockwise direction.
It is given that AB = CD. Also, the adjacent angles A and D are supplementary.
If a four sided polygon has a set of opposite sides that are equal in length and if the adjacent angles are supplementary, the polygon is a parallelogram.
The figure in the link provided is a parallelogram.