{"id":5954,"date":"2021-10-04T17:55:15","date_gmt":"2021-10-04T12:25:15","guid":{"rendered":"https:\/\/mathemerize.com\/?p=5954"},"modified":"2022-03-06T14:15:33","modified_gmt":"2022-03-06T08:45:33","slug":"involutory-matrix","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/involutory-matrix\/","title":{"rendered":"Involutory Matrix – Definition and Examples"},"content":{"rendered":"
Here you will learn what is involutory matrix with examples.<\/p>\n
Let’s begin –<\/p>\n
\nIf \\(A^2\\) = I . the matrix A is said to be an involutory matrix, i.e. the square roots of the identity matrix (I) is involutory matrix.<\/p>\n
Note : The determinant value of this matrix (A) is 1 or -1.<\/p>\n<\/blockquote>\n
Example<\/span><\/strong> : Show that the matrix A = \\(\\begin{bmatrix} -5 & -8 &\u00a0 0 \\\\\u00a0 3 & 5 & 0 \\\\\u00a0 1 & 2 & -1 \\end{bmatrix}\\) is involutory.<\/p>\n
Solution<\/span><\/strong> : We have,<\/p>\n
A = \\(\\begin{bmatrix} -5 & -8 &\u00a0 0 \\\\\u00a0 3 & 5 & 0 \\\\\u00a0 1 & 2 & -1 \\end{bmatrix}\\)<\/p>\n
Now we find, \\(A^2\\) = A . A<\/p>\n
\\(\\implies\\) \\(A^2\\) = \\(\\begin{bmatrix} -5 & -8 &\u00a0 0 \\\\\u00a0 3 & 5 & 0 \\\\\u00a0 1 & 2 & -1 \\end{bmatrix}\\) \\(\\times\\) \\(\\begin{bmatrix} -5 & -8 &\u00a0 0 \\\\\u00a0 3 & 5 & 0 \\\\\u00a0 1 & 2 & -1 \\end{bmatrix}\\)<\/p>\n
= \\(\\begin{bmatrix} 1 & 0 &\u00a0 0 \\\\\u00a0 0 & 1 & 0 \\\\\u00a0 0 & 0 & 1 \\end{bmatrix}\\)<\/p>\n
Hence, the given matrix A is involutary.<\/p>\n
Example<\/span><\/strong> : Show that the sqare matrix A is involutary, iff (I – A) (I + A) = O<\/p>\n
Solution<\/span><\/strong> : Let A is the involutary matrix,<\/p>\n
Then, \\(A^2\\) = I<\/p>\n
(I – A) (I + A) = \\(I^2\\) + IA – AI – \\(A^2\\)<\/p>\n
= I + A – A – \\(A^2\\)\u00a0<\/p>\n
= I – \\(A^2\\) = O<\/p>\n
Conversely, let (I – A) (I + A) = O<\/p>\n
\\(\\implies\\) \\(I^2\\) + IA – AI – \\(A^2\\) = O<\/p>\n
\\(\\implies\\) I + A – A – \\(A^2\\) = O<\/p>\n
= I – \\(A^2\\) = O<\/p>\n
Hence, the given matrix A is involutary.<\/p>\n\n\n