Explanation:
The area of the triangle formed by the vertices $\mathrm{A}(1,-1),\mathrm{B}(-4,6)$ and $\mathrm{C}(-3,-5)$, by using the formula above, is given by
$\displaystyle \dfrac{1}{2}$ ​[1(6 + 5) + ( − 4)( − 5 + 1) + ( − 3)( − 1 − 6)]
=$\displaystyle \dfrac{1}{2}$ (11 + 16 + 21) = 24
So, the area of the triangle is 24 square units.