T451

f(x) = tan(x) - x
f' = Derivative(f)
A = Intersect(f', xAxis, (-3.1415920944846745, 3.1259853383439E-13))
B = Intersect(f', xAxis, (3.141591683982871, 9.401375840247352E-13))
C = Intersect(f', xAxis, (0, 0))
g: y = (-x)