For lines to be perpendicular their slopes must be negative reciprocals of one another, mathematically:
m1*m2=-1
So we first need to find the slope of the reference line.
m=(y2-y1)/(x2-x1)=(7-2)/(-1--5)=5/4
So the perpendicular line will have a slope of:
5m/4=-1
m=-4/5
So our perpendicular line so far is:
y=-4x/5+b, now we can use point (3,-1) to solve for the y-intercept, "b"
-1=-4(3)/5+b
-1=-12/5+b
-5/5+12/5=b
7/5=b
So the line is:
y=-4x/5+7/5 or more neatly
y=(-4x+7)/5
y=-0.8x+1.4
