# Size of a triangle using determinant [duplicate]

find the size of a triangle using (determinant) with the following points:
$(x_1,y_1)=(1,-2)$
$(x_2,y_2)=(-4,-2)$
$(x_3,y_3)=(-5,-1)$

How should I place those points in the determinant? or firstly in a matrix?

$A=\frac{1}{2}abs\left(\begin{vmatrix} x_{1} & y_{1}& 1\\ x_{2} & y_{2}& 1\\ x_{3} & y_{3}& 1 \end{vmatrix}\right)$