xll := BinSearch(f, LEFT_BOUND_F, BinSearch(df, LEFT_BOUND_DF, x1));
xrr := BinSearch(f, BinSearch(df, x2, RIGHT_BOUND_DF), RIGHT_BOUND_F);

p := -xll - xrr;
q := xll * xrr;

x3 := (p - a) / 2 + sqrt(sqr((a - p) / 2) + q - b + p * (a - p));
x4 := (p - a) / 2 - sqrt(sqr((a - p) / 2) + q - b + p * (a - p));