[tex]\bf \textit{distance between 2 points}\\ \quad \\
\begin{array}{lllll}
&x_1&y_1&x_2&y_2\\
% (a,b)
C&({{ 1}}\quad ,&{{ 9}})\quad
% (c,d)
B&({{ 7}}\quad ,&{{ 1}})
\end{array}\qquad
% distance value
d = \sqrt{({{ x_2}}-{{ x_1}})^2 + ({{ y_2}}-{{ y_1}})^2}
\\\\\\
CB=\sqrt{(7-1)^2+(1-9)^2}\implies CB=\sqrt{6^2+(-8)^2}
\\\\\\
CB=\sqrt{36+64}\implies CB=\sqrt{100}\implies CB=10[/tex]
add the sides with 8 and 6 to it, and that's the perimeter.
