A line is drawn from a point `P(x, y)` on the curve `y = f(x),` making an angle with the x-axis which is supplementary to the one made by the tangent to the curve at `P(x, y).` The line meets the x-axis at A. Another line perpendicular to it drawn from `P(x, y)` meeting the y-axis at B. If `OA = OB,` where `O` is the origin, the equation of all curves which pass through (`1, 1)` is