Write an equation in point-slope form for the perpendicular bisector of the segment with endpoints m(-1,-3) and n(7,1)

To find the perpendicular bisector, you have to find the midpoint of mn
which is

 <-- midpoint of mn

next you find the slope of mn which is
 
<- this is the slope

to find the perpendicular slope, you take the negative recipricol which is

-2

so now we know the perpendicular bisector line has a slope of -2 and passes through (-4, -2)

so 

y-(-2) = -2(x-(-4))