\( \left[\begin{array}{lll}1 & 1 & 2 \\ 3 & 2 & 1 \\ 1 & 2 & 3\end{array}\right] \) find the Rank of matrix
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To find the rank of the given matrix, we begin by reducing it to its row echelon form (REF) or reduced row echelon form (RREF). The given matrix is: \[ \begin{bmatrix} 1 & 1 & 2 \\ 3 & 2 & 1 \\ 1 & 2 & 3 \end{bmatrix} \] We can perform row operations. Starting with the first row, we can eliminate the leading coefficients in the second and third rows. 1. Subtract 3 times the first row from the second row: \[ R_2 \rightarrow R_2 - 3R_1 \Rightarrow 3 - 3(1), 2 - 3(1), 1 - 3(2) \Rightarrow [0, -1, -5] \] 2. Subtract the first row from the third row: \[ R_3 \rightarrow R_3 - R_1 \Rightarrow 1 - 1, 2 - 1, 3 - 2 \Rightarrow [0, 1, 1] \] Now, the matrix looks like this: \[ \begin{bmatrix} 1 & 1 & 2 \\ 0 & -1 & -5 \\ 0 & 1 & 1 \end{bmatrix} \] Next, we can simplify the second row by multiplying it by -1, and then eliminate the leading coefficient in the third row: 3. Multiply the second row by -1: \[ R_2 \rightarrow -R_2 \Rightarrow [0, 1, 5] \] Now we have: \[ \begin{bmatrix} 1 & 1 & 2 \\ 0 & 1 & 5 \\ 0 & 1 & 1 \end{bmatrix} \] 4. Subtract the second row from the third row: \[ R_3 \rightarrow R_3 - R_2 \Rightarrow [0, 1 - 1, 1 - 5] \Rightarrow [0, 0, -4] \] Now the matrix is: \[ \begin{bmatrix} 1 & 1 & 2 \\ 0 & 1 & 5 \\ 0 & 0 & -4 \end{bmatrix} \] Since there are three non-zero rows, the rank of the matrix is 3. Thus, the rank of the given matrix is **3**.
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