Set 9: Quadratic Equations

Choice A is correct. Choice A is the correct answer. This is a perfect square trinomial: $x^2 - 16 x + 64 = (x - 8)^2$. Check: first term $x^2 = (x)^2$ ✓, last term $64= 8^2$ ✓, middle term $-16 x = -2(x)(8)$ ✓. Pattern: $a^2 - 2 ab + b^2 = (a - b)^2$. Choice B is incorrect because $(x + 8)^2 = x^2 + 16 x + 64$ (positive middle term). Choice C is incorrect because $(x - 16)(x - 4) = x^2 - 20 x + 64$ (wrong middle coefficient). Choice D is incorrect because this is difference of squares pattern, giving $x^2 - 64$.