Aufgabe: Linear Mapping and matrix
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Which of the following maps are linear?
\( \begin{array}{l} \vee \mathbb{R}^{2} \rightarrow \mathbb{R} \text { with }\left(\begin{array}{l} x_{1} \\ x_{2} \end{array}\right) \mapsto\left(x_{1} \cdot x_{2}\right) \\ \vee \mathbb{R}^{2} \rightarrow \mathbb{R}^{2} \text { with }\left(\begin{array}{l} x_{1} \\ x_{2} \end{array}\right) \mapsto\left(\begin{array}{c} x_{1} \cdot x_{2} \\ x_{1}+x_{2} \end{array}\right) \\ \vee \mathbb{R}^{2} \rightarrow \mathbb{R}^{2} \text { with }\left(\begin{array}{l} x_{1} \\ x_{2} \end{array}\right) \mapsto\left(\begin{array}{l} -1 x_{1}-1 x_{2} \\ -2 x_{1}+2 x_{2} \end{array}\right) \end{array} \)
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For which value of \( \alpha \in \mathbb{R} \) is the rank of the following matrix equal to 2 ?
\( \left(\begin{array}{ccc} -4 & -4 & 4 \\ 3 & -21 & 9 \\ 1 & \alpha & 0 \end{array}\right) \)
Answer: \( \alpha= \)
Problem/Ansatz: kann mir hier einer helfen, ich habe viele Rechnung gemacht aber die Lösung sind immer wieder falsch?