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UKMT Senior Mathematical Challenge, 2021

Algebra Difficulty 3.0 AMC 10/12 Find the answer United Kingdom

Let $x$ be a real number. What is the minimum value of $(x^2 - 4x + 3)(x^2 + 4x + 3)$ ?

(A) $-16$ (B) $-9$ (C) $0$ (D) $9$ (E) $16$

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