The best way to answer this question is using Pythagoras' Theorem $a^2 + b^2 = c^2$ and a sketch.

$$\begin{split} &\, a^2 + b^2 = c^2 \\  &\,  (\var{bx} - \var{ax})^2 + (\var{by} - \var{ay})^2 = c^2 \\ &\, (\var{bx-ax})^2 + (\var{by-ay})^2 = c^2 \\ &\, \var{(ax-bx)^2 + (ay-by)^2} = c^2 \\  &\,\sqrt{\var{(ax-bx)^2 + (ay-by)^2}}= c \\ &\,\var{sqrt((ax-bx)^2 + (ay-by)^2)}= c \\ &\, c = \var{csimp}  \text{ units} \\ \end{split}$$