Question 491981
We will use the distance formula to find the distance between vertices.
{{{sqrt((x2 - x1)^2 + (y2 - y1)^2)}}}

AB = {{{sqrt((1 - -2 )^2 + (3 - 5)^2)}}}
AB = {{{sqrt((3)^2 + (2)^2)}}}
AB = {{{sqrt(13)}}}
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BC = {{{sqrt((-1 - -1)^2 + (0 - 3)^2)}}}
BC = {{{sqrt((2)^2 + (3)^2)}}}
BC = {{{sqrt(13)}}}
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AC = {{{sqrt((-1 - -2)^2 + (0 - 5)^2)}}}
AC = {{{sqrt((1)^2 + (5)^2)}}}
AC = {{{sqrt(26)}}}
Ac = {{{sqrt(2)}}}{{{sqrt(13)}}}
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At this point, I converted to decimals, they are easier to work with.
AC = 3.6
BC = 3.6
AC = 5.1
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Now, we use Herons formula to find the area.
Area = {{{sqrt(s(s-a)(s-b)(s-c))}}}
s = (3.6 + 3.6 + 5.1) / 2
s = 12.3/ 2 =6.15
Area = {{{sqrt(6.15)(2.55)(2.55)(1.05))}}}
Area = {{{sqrt(19.28)}}}
Area = 4.4
Cleomenius.