Choice A is the correct answer. The discriminant formula is $\Delta = b^2 - 4ac$.

1. Identify coefficients: $a=1, b=4, c=4$.
2. Substitute: $\Delta = 4^2 - 4(1)(4)$.
3. Calculate: $16 - 16 = 0$.

A discriminant of 0 indicates that the quadratic has exactly one real solution (a repeated root).

Choice B is incorrect because it calculates $b^2$ only. Choice C is incorrect because it adds $4ac$ instead of subtracting ($16+16$). Choice D is incorrect because it subtracts in reverse order ($4ac - b^2$).