The determinant of a matrix is a special number that can be calculated from the matrix. It tells us things about the matrix that are useful in system of line link in calculus and more.
The symbol |A|
First of all the matrix must be square( have the same number of rows as columns). Then it is just a matter of basic arithmetic.
Let we have
[a b]
[c d]
then the determinant |A|=ab=cd
Know more about
Determinant of Symmetric Matrix