Which of these equations has a graph that is tangent to the x-axis at one of its intercepts? Choose all the polynomials that have this property.
y = x^2 + 6x + 9
y = –x^3
y = (x + 2)(x + 6)^2
y = (x – 5)(x + 3)(x + 1)(x – 5)
y = x^4