What is the completely factored form of x2 – 16xy + 64y2?

Recognize x² – 16xy + 64y² as a perfect-square trinomial: x² – 2(x)(8y) + (8y)². Using a² – 2ab + b² = (a – b)², it factors to (x – 8y)(x – 8y). Choice C gives this factorization.

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