Matrices

Concept:A matrix where all entries above the main diagonal are zero is called a lower triangular matrix.Explanation:The given matrix is $\begin{bmatrix} 3 & 0 & 0 \\ 2 & 5 & 0 \\ 1 & 2 & 6 \end{bmatrix}$.Observe that all elements above the main diagonal (positions $(1,2)$, $(1,3)$, $(2,3)$) are $0$.Hence, it satisfies the definition of a lower triangular matrix.It is not an identity matrix (diagonal entries are not all $1$).It is not skew-symmetric (since $A^T \neq -A$).It is not a diagonal matrix (there are non-zero entries below the diagonal).Answer:Lower triangular matrix