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The determinant is computed using the standard $2\times 2$ rule $ad - bc$. For the matrix $A = \begin{bmatrix} 3 & 1 \\ 1 & 2 \end{bmatrix}$, this means multiplying the main diagonal entries ($3 \cdot 2$) and subtracting the product of the off-diagonal entries ($1 \cdot 1$).

Conditions: The matrix is $2\times 2$.; Entries are real numbers.

The determinant is computed using the standard $2\times 2$ rule $ad - bc$. For the matrix $A = \begin{bmatrix} 3 & 1 \\ 1 & 2 \end{bmatrix}$, this means multiplying the main diagonal entries ($3 \cdot 2$) and subtracting the product of the off-diagonal entries ($1 \cdot 1$).

Conditions: The matrix is $2\times 2$.; Entries are real numbers.