Qual matriz representa?

\[\eqalign{ B^{-1}&= \begin{bmatrix} a&b\\c&d \end{bmatrix}^{-1} \\ &= {1 \over ad-bc}\cdot\begin{bmatrix} d&-b\\-c&a \end{bmatrix} \\ }\]

Considerando \(a=-1\) \(b=6\) \(c=0\)e \(d=9\) a inversa da matriz \(B= \begin{bmatrix} -1&6\\0&9 \end{bmatrix}\)é:

\[\eqalign{ B^{-1}&= \begin{bmatrix} -1&6\\0&9 \end{bmatrix}^{-1} \\ &= {1 \over -1\cdot 9-6\cdot 0}\cdot\begin{bmatrix} 9&-6\\-0&-1 \end{bmatrix} \\ &= {1 \over -9-0}\cdot\begin{bmatrix} 9&-6\\0&-1 \end{bmatrix} \\ &= {1 \over -9}\cdot\begin{bmatrix} 9&-6\\0&-1 \end{bmatrix} \\ &= {1 \over 9}\cdot\begin{bmatrix} -9&6\\0&1 \end{bmatrix} \\ }\]

Resposta correta: alternativa a) \(B^{-1}={1 \over 9}\cdot\begin{bmatrix} -9&6\\0&1 \end{bmatrix}\)