[tex]\bf \textit{distance between 2 points}\\ \quad \\
\begin{array}{lllll}
&x_1&y_1&x_2&y_2\\
% (a,b)
R&({{ 7.7}}\quad ,&{{ 9.9}})\quad
% (c,d)
S&({{ -5.7}}\quad ,&{{ -4.9}})
\end{array}\qquad
% distance value
d = \sqrt{({{ x_2}}-{{ x_1}})^2 + ({{ y_2}}-{{ y_1}})^2}
\\\\\\
RS=\sqrt{(-5.7-7.7)^2+(-4.9-9.9)^2}\implies RS=\sqrt{(-13.4)^2+(-14.8)^2}
\\\\\\
RS=\sqrt{179.56+219.04}\implies RS=\sqrt{398.6}\implies RS\approx 19.96496932[/tex]
