[tex]\text{The formula of a distance between two points}\\\\A(x_A;\ y_A);\ B(x_B;\ y_B)\\\\|AB|=\sqrt{(x_B-x_A)^2+(y_B-y_A)^2}\\\\\text{We have}\ R(-1;\ 1);\ S(-4;\ -5)\\\\\text{substitute}\\\\|RS|=\sqrt{(-4-(-1))^2+(-5-1)^2}=\sqrt{(-3)^2+(-6)^2}\\\\=\sqrt{9+36}=\sqrt{45}\approx6.7\\\\\text{Answer: 6.7}[/tex]
