###### Itema

Which of the following equations are linear? Please provide a justification for your response.

1. \begin{equation*} 2x + xy -3y^2 = 2 \text{.} \end{equation*}
2. \begin{equation*} -2x_1 + 3x_2 +4x_3 - x_5 = 0 \text{.} \end{equation*}
3. \begin{equation*} x = 3z - 4y \text{.} \end{equation*}
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