### Algebra: Variables

### Substitution

Substitution

If a variable occurs in an expression, you can enter any number for that variable. In other words: replace every occurence of that variable in the expression by a number. This process is called |
Calculate #\blue{x}^2+\blue{x}# for #\blue{x}=\green{3}#: \[{\blue{x}^2+\blue{x}=}{\green{3}^2+\green{3}}{=12}\] |

#17#

#\begin{array}{rcl}

\displaystyle x^2+x+5 &=& \displaystyle3^2+3+5 \\

&&\blue{\text{\(x\) replaced with \(3\)}}\\

&=& \displaystyle 17 \\

&&\blue{\text{calculated}}\\

\end{array}#

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