How to find the algebraic covalent of the second order determinant For example, 3 1 2 1 His adjoint matrix Don't you have to find his algebraic cofactor? I can find the third order or higher order, but not the second order I'm learning linear algebra by myself

How to find the algebraic covalent of the second order determinant For example, 3 1 2 1 His adjoint matrix Don't you have to find his algebraic cofactor? I can find the third order or higher order, but not the second order I'm learning linear algebra by myself

The answer is in the picture below:

What is the covalent of first order determinant algebra?

The covalent of first order determinant algebra is 1

Determinant calculation
a b c 1
b c a 1
c a b 1
(b+c)/2 (c+a)/2 (a+b)/2 1

The answer is 0
Add the elements of the second column and the third column to the first column, and the value of the determinant remains unchanged. At this time, the elements of the first column become a + B + C. at this time, the first column is proportional to the corresponding elements of the last column. The determinant is 0