A child is standing across the street from his apartment. His mother is on their balcony. The angle of elevation between the chi
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ANSWER
24
EXPLANATION
For a matrix A of order n×n, the cofactor of element
is defined to be
is the minor of element
equal to the determinant of the matrix we get by taking matrix A and deleting row i and column j.
Here, we have
M₁₁ is the determinant of the matrix that is matrix A with row 1 and column 1 removed. The bold entries are the row and the column we delete.
Since the determinant of a 2×2 matrix is
it follows that
so