When one quantity (e.g. \(x\)) represents a function (e.g. \(a + b\)), we can replace, or substitute, the function into an equation containing this quantity.
Multiple equations describing the same situation often arise in Mechanics (an elastic colllision provides equations for momentum and kinetic energy) or Electricity (Kirchhoff's laws for current and potential difference). We can solve them simultaneously.
Key Concepts
This video demonstrates some examples of how to substitute from one equation into another.
If two or more variables are contained in two or more equations, it might be possible to solve them simultaneously. Just as one variable can be found from one equation (e.g. \(3a=15-3\)):
- Two equations can be used to find two variables, provided that no other variables are present
- Three equations can be used to find three variables
How much of Algebraic techniques have you understood?
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