JEE MAIN - Mathematics (2023 - 13th April Morning Shift - No. 15)
Explanation
Sure! A symmetric matrix is a square matrix that is equal to its transpose. For a matrix to be symmetric, the element at row i and column j must be equal to the element at row j and column i. In other words, $$A_{ij} = A_{ji}$$.
For a 3 $$ \times $$ 3 symmetric matrix, it looks like this:
$$ \begin{pmatrix} a & b & c \\ b & d & e \\ c & e & f \\ \end{pmatrix} $$
Notice that there are only 6 unique elements we need to fill because of the symmetry:
- $$a$$ in the (1,1) position
- $$b$$ in the (1,2) and (2,1) positions
- $$c$$ in the (1,3) and (3,1) positions
- $$d$$ in the (2,2) position
- $$e$$ in the (2,3) and (3,2) positions
- $$f$$ in the (3,3) position
Each of these unique elements can take a value from the set $${0,1,2,3,4,5,6,7,8,9}$$, which has 10 elements.
We have 10 choices for each of the 6 unique elements, so the total number of symmetric matrices can be calculated as:
$$10 \times 10 \times 10 \times 10 \times 10 \times 10 = 10^{6}$$
Thus, the total number of symmetric matrices of order 3 with entries from this set is $$10^{6}$$.
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