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If A=[1000−10001]A = \begin{bmatrix} 1 & 0 & 0 \\ 0 & -1 & 0 \\ 0 & 0 & 1 \end{bmatrix} then A−1A^{-1} is equal to

Solution

✅ Correct Option: 4

The given matrix A=[1000−10001]A = \begin{bmatrix} 1 & 0 & 0 \\ 0 & -1 & 0 \\ 0 & 0 & 1 \end{bmatrix} is a diagonal matrix.

For a diagonal matrix, the inverse is found by taking the reciprocal of each diagonal element.

The diagonal elements of AA are: 1,−1,11, -1, 1

Their reciprocals are:

11=1\frac{1}{1} = 1

1−1=−1\frac{1}{-1} = -1

11=1\frac{1}{1} = 1


Therefore:

A−1=[1000−10001]A^{-1} = \begin{bmatrix} 1 & 0 & 0 \\ 0 & -1 & 0 \\ 0 & 0 & 1 \end{bmatrix}

Note that A−1=AA^{-1} = A, meaning AA is its own inverse.

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