Bibliography:
- http://www.coolmath.com/reference/parallelograms.html
- http://www.dummies.com/how-to/content/properties-of-parallelograms.html
- http://answers.yahoo.com/question/index?qid=20090119062849AACvJIC
- http://www.mmsonline.com/columns/what-good-is-aparallelogram
- http://www.glogster.com/agalexander0629/addie-alexander-geometry-project/g-6n893o8ombvo122r170pooa
- http://www.algebra.com/algebra/homework/word/geometry/How-to-solve-problems-on-the-angles-of-parallelograms.lesson
- http://library.thinkquest.org/C006354/pictures.html
- http://en.wikipedia.org/wiki/Parallelogram_law
- http://www.mathsisfun.com/geometry/parallelogram.html
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http://www.mathwarehouse.com/geometry/quadrilaterals/parallelograms/interactive-parallelogram.php