The perpendicular bisector of line segment $\overline{ab}$ is the line that passes through the midpoint of $\overline{ab}$ and is perpendicular to $\overline{ab}$. What is an equation for the perpendicular bisector of the line segment joining $(1,2)$ and $(-5,12)$? write your equation in point-slope form, standard form, or slope-intercept form.