well, we know is an EQUIlateral triangle, so all 3 sides are equal, so hmmm we can just get the distance between those two vertices and triple it for its perimeter.
[tex]~~~~~~~~~~~~\textit{distance between 2 points} \\\\ (\stackrel{x_1}{-8}~,~\stackrel{y_1}{-5})\qquad (\stackrel{x_2}{3}~,~\stackrel{y_2}{7})\qquad \qquad d = \sqrt{( x_2- x_1)^2 + ( y_2- y_1)^2} \\\\\\ d=\sqrt{[3 - (-8)]^2 + [7 - (-5)]^2}\implies d=\sqrt{(3+8)^2 + (7+5)^2} \\\\\\ d=\sqrt{265}\implies \stackrel{triple~that}{3\sqrt{265}} ~~ \approx ~~ 48.84[/tex]
