the perimeter of the triangle, will be the lengths of all segments,
making it up, so.. find the lengths of segments AB, BC and CA,
and sum them up
[tex]\textit{distance between 2 points}\\ \quad \\
\begin{array}{lllll}
&x_1&y_1&x_2&y_2\\
% (a,b)
&A({{ 1}}\quad ,&{{ 1}})\quad
% (c,d)
&B({{ 7}}\quad ,&{{ 1}})\\
&B({{ 7}}\quad ,&{{ 1}})\quad
% (c,d)
&C({{ 1}}\quad ,&{{ 9}})\\
&C({{ 1}}\quad ,&{{ 9}})\quad
% (c,d)
&A({{ 1}}\quad ,&{{ 1}})\\
\end{array}\qquad
% distance value
d = \sqrt{({{ x_2}}-{{ x_1}})^2 + ({{ y_2}}-{{ y_1}})^2}[/tex]
