The slope of AB is (0-4)/(-2-0)=2, so since perpendicular lines have negative reciprocal slopes, the slope of the perpendicular line is -0.5.
So, the equation of the line is:
y + 1 = -0.5(x - 5)
y + 1 = -0.5x + 2.5
y = -0.5x + 1.5
