The graph of a quadratic function touches, but does not cross, the x-axis at x = 4. which function represents this situation?

When a zero of a function does not cross the x-axis but touches it, this means that the zero is a "double root". It has two of the same factor (x - 4)^2 and two of the same zeros, x = 4 and x = 4
f(x) = x^2 - 8x + 16 would be the function with a double root at 4