Find the slope of the tangent line to the graph of f at any given point
f(x) = -2x + 6 at (2,2)
The slope of the f(x) graph, which is itself a straight line, is -2. The slope of a line perpendicular to f(x) must therefore be +1/2.
The equation of the perpendicular line is
(y-2) = (1/2)(x-2)
y = 2 + (x/2) -1 = (x/2) +1