Determinant of Transpose

Theorem
Let $\mathbf A = \left[{a}\right]_{n}$ be a square matrix of order $n$.

Let $\det \left({\mathbf A}\right)$ be the determinant of $\mathbf A$.

Let $\mathbf A^\intercal$ be the transpose of $\mathbf A$.

Then $\det \left({\mathbf A}\right) = \det \left({\mathbf A^\intercal}\right)$.

Proof
Let $\mathbf A = \begin{bmatrix} a_{11} & a_{12} & \ldots & a_{1n} \\ a_{21} & a_{22} & \cdots & a_{2n} \\ \vdots & \vdots & \ddots & \vdots \\ a_{n1} & a_{n2} & \cdots & a_{nn} \\ \end{bmatrix}$.

Then $\mathbf A^\intercal = \begin{bmatrix} a_{11} & a_{21} & \ldots & a_{n1} \\ a_{12} & a_{22} & \cdots & a_{n2} \\ \vdots & \vdots & \ddots & \vdots \\ a_{1n} & a_{2n} & \cdots & a_{nn} \\ \end{bmatrix}$.

Let $b_{rs} = a_{sr}$ for $1 \le r, s \le n$.

We need to show that $\det \left({\left[{a}\right]_{n}}\right) = \det \left({\left[{b}\right]_{n}}\right)$.

By the definition of determinant and Permutation of Determinant Indices, we have:

Comment
Thus there is symmetry between rows and columns of a determinant.

So, if we can prove something about a determinant's rows, it follows that this also applies to the determinant's columns, and vice versa.