Question

Calculati aria triunghiului ABC ,stiind ca A(1,2) B(-2,1) si C(O ,-1)

Answer 1

$S_{ABC}=\frac{1}{2}| \left|\begin{array}{ccc}x_A&y_A&1\\x_B&y_B&1\\x_C&y_C&1\end{array}\right||=\frac{1}{2}| \left|\begin{array}{ccc}1&2&1\\-2&1&1\\0&-1&1\end{array}\right|| =\frac{8}{2}=4$

Answer 2

$1/2\left[\begin{array}{ccc}1&2&1\\-2&1&1\\0&-1&1\end{array}\right]$=
8/2=4