Area of a triangle with points at (-9,5), (6,10), and (2,-10)

First we are going to draw the triangle using the given coordinates. 
Next, we are going to use the distance formula to find the sides of our triangle.
Distance formula: 

Distance from point A to point B:







Distance from point A to point C:







Distance from point B from point C






Now, we are going to find the semi-perimeter of our triangle using the semi-perimeter formula:





Finally, to find the area of our triangle, we are going to use Heron's formula:





We can conclude that the perimeter of our triangle is 140.13 square units.