[tex]\bf ~~~~~~~~~~~~\textit{distance between 2 points}
\\\\
(\stackrel{x_1}{9}~,~\stackrel{y_1}{8})\qquad
(\stackrel{x_2}{1}~,~\stackrel{y_2}{-2})\qquad \qquad
% distance value
d = \sqrt{( x_2- x_1)^2 + ( y_2- y_1)^2}
\\\\\\
d=\sqrt{(1-9)^2+(-2-8)^2}\implies d=\sqrt{(-8)^2+(-10)^2}
\\\\\\
d=\sqrt{64+100}\implies d=\sqrt{164}\implies d=\sqrt{4\cdot 41}\implies d=\sqrt{2^2\cdot 41}
\\\\\\
d=2\sqrt{41}[/tex]
