Set 9: Quadratic Equations (Advanced)

Choice A is correct. Choice A is the correct answer. For exactly one real solution, the discriminant must be zero ($\Delta = 0$). 1. Set $b^2 - 4 ac = 0$. 2. $6^2 - 4(1)(k) = 0$. 3. $36- 4 k = 0$. 4. $36= 4 k \Rightarrow k = 9$. Choice B is incorrect because it is $b^2$. Choice C is incorrect because it is $b/2$. Choice D is incorrect because $k$ must be positive.