to find the perpendicular bisector, you have to find the midpoint of mn
which is
\(( \frac{-1 -7}{2} , \frac{-3 -1}{2} ) = (-4, -2)\) <-- midpoint of mn
next you find the slope of mn which is
\(\frac{-3 -1}{-1 -7} = \frac{-4}{-8} = 1/2\) <- 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))
