Answer
$\sqrt 192.58\approx13.877$ units
Work Step by Step
We know that the distance $d$ between two points $(x_{1},y_{1})$ and $x_{2},y_{2})$ is given by $d=\sqrt ((x_{2}-x_{1})^{2}+(y_{2}-y_{1})^{2})$.
Therefore, the distance between $(1.7,-3.6)$ and $(-8.6,5.7)$ will be $d=\sqrt ((-8.6-1.7)^{2}+(5.7-(-3.6))^{2})=\sqrt ((-10.3)^{2}+(9.3)^{2})=\sqrt (106.09+86.49)=\sqrt 192.58\approx13.877$ units