inverse

P and Q are two square matrices of the same order. Which of the following statement(s) is/are correct?

The inverse of the matrix $\begin{bmatrix} 2 & 3 & 4 \\ 4 & 3 & 1 \\ 1 & 2 & 4 \end{bmatrix}$ is

The matrix P is the inverse of a matrix Q. If I denotes the identity matrix, which one of the following options is correct?

For the given orthogonal matrix Q, Q = [3/7 2/7 6/7; -6/7 3/7 2/7; 2/7 6/7 -3/7]. The inverse is