GeoGebra CAS (Symbolic Calculation)
1 http://youtu.be/SqcmGZai6Zk
2: Solving System of Equations
http://youtu.be/wIUezT7gC90
3: Solving Simultaneous Equations by Elimination
http://youtu.be/mUBns5z8yMw
4: Solving Simultaneous Equations by Substitution
http://youtu.be/20XqJoJ5sxI
5: Solving Simultaneous Equations Algebraically and Graphically
http://youtu.be/FaptneTlmgM