Question

Please help! Correct answer only, please! Consider the matrix shown below: Using your calculator find the inverse of the matrix Q (i.e. Find Q^-1).

Answer 1

Answer: C

Explanation:

In order to find the inverse, transpose the matrix then find the determinant of each 2 x 2 matrix within it.

`Q=\left[\begin{array}{ccc}2&2&3\\1&1&1\\3&2&1\end{array}\right] \qquad \rightarrow \qquad Q^T=\left[\begin{array}{ccc}2&1&3\\2&1&2\\3&1&1\end{array}\right]`

`det\left[\begin{array}{cc}1&2\\1&1\end{array}\right] =\bold{-1}\qquad det\left[\begin{array}{cc}2&2\\3&1\end{array}\right]=\bold{-4}\qquad det\left[\begin{array}{cc}2&1\\3&1\end{array}\right] =\bold{-1}\\\\\\\\det\left[\begin{array}{cc}1&3\\1&1\end{array}\right] =\bold{-2}\qquad det\left[\begin{array}{cc}2&3\\3&1\end{array}\right]=\bold{-7}\qquad det\left[\begin{array}{cc}2&1\\3&1\end{array}\right] =\bold{-1}\\`

`det\left[\begin{array}{cc}1&3\\1&2 \end{array}\right] =\bold{-1}\qquad det\left[\begin{array}{cc}2&3\\2&2\end{array}\right]=\bold{-2}\qquad det\left[\begin{array}{cc}2&1\\2&1\end{array}\right] =\bold{0}`

`Q^(-1)=\large\left[\begin{array}{ccc}1&-4&1\\-2&7&-1\\-1&-2&0\end{array}\right]`