Question 490090
We can use the distance formula to find the area between coordinates.
{{{sqrt((x2 - x1)^2 + (y2 - y1)^2)}}}
AB = {{{sqrt((-2 -(-5))^2 + (5 - 1)^2)}}}
AB = {{{sqrt(25)}}} = 5 
BC = {{{sqrt((1 - (-2))^2 + (1 - 5)^2)}}}
BC = {{{sqrt(25)}}} = 5 
AC = {{{sqrt((1 - (-5))^2 + (1 - 1)^2)}}}
AC = {{{sqrt(36 )}}} = 6
So this will give us the length of the sides
AC = 5
BC = 5
AC = 6
The perimeter therefore will be 5 + 5 + 6 = 16 
The area we can find using Herons formula.
Area = {{{sqrt(s(s-a)(s-b)(s-c))}}}
Where s is the semiperimeter of the triangle.
 s = 5 + 5 + 6/ 2 = 8


{{{sqrt(8(3)(3)(2))}}}
Area = {{{sqrt(144)}}}
Area = 12
A good website that explains this formula is:
http://www.mathsisfun.com/geometry/herons-formula.html
Cleomenius.