Note
Two tangents to the curve y = f(x) will be
(i) parallel if the slopes are equal and
(ii) perpendicular to each other if the product of their slopes is -1.
3.3.3 Equation of the Normal
The line which is perpendicular to the tangent at the point of
contact P(x, y) is called normal.
The equation of the normal at (x1
, y1
) is