First you need to rewrite the equation in the form y = mx +b:
2y = x-4
Divide all terms by 2:
2y / 2 = x/2 - 4/2
Simplify:
y = 1/2x - 2
The slope of the line is 1/2.
A perpendicular line has a slope of the negative reciprocal, which would be -2.
Now using the point slope method:
y - y1 = m(x-x1)
Using the given point of (8,-4) and m = -2
you get:
y +4 = -2(x-8)
Simplify:
y +4 = -2x +16
Now subtract 4 from both sides to get the final equation:
y = -2x +12
