Inverse Matrix

Inverse Matrix

IP 3

For any \(2\times2\) matrix \(\mathbf{A} = \begin{pmatrix} a & b \\ c & d \end{pmatrix}\), where \(a\), \(b\), \(c\) and \(d\) are real numbers, the determinant of \(\mathbf{A}\) is denoted by

\(|\mathbf{A}| = ad - bc.\)

If \(|\mathbf{A}| \neq 0\), the inverse matrix of \(\mathbf{A}\) denoted by

\(\mathbf{A}^{-1} = \frac{1}{|\mathbf{A}|} \begin{pmatrix} d & -b \\ -c & a \end{pmatrix} = \frac{1}{ad - bc} \begin{pmatrix} d & -b \\ -c & a \end{pmatrix},\)

such that \(\mathbf{AA}^{-1} = \mathbf{A}^{-1}\mathbf{A} = \mathbf{I}\), where \(\mathbf{I}\) is the identity matrix.

  1. Find the inverse of: \(\mathbf{A} = \begin{pmatrix} 2 & 1 \\ 5 & -3 \end{pmatrix}\).
  2. Hence, solve the system of equations
    \(\begin{aligned} 2x + y &= 5 \\ 5x - 3y &= 7 \end{aligned}\)

Solution:

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Answer:(i) \(A^{-1}=\frac1{11}\begin{pmatrix}3&1\\5&-2\end{pmatrix}\); (ii) \(x=2,y=1\).

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