Answer
$(2x-1)^{2}$
Work Step by Step
Expression : $1 - 4x + 4x^{2} = (2x)^{2} - 4x + 1^{2}$
By the well known formula $(a-b)^{2} = a^{2} -2ab + b^{2}$
Hence, $1 - 4x + 4x^{2} = (2x)^{2} - 2(2x)(1) + 1^{2} = (2x-1)^{2}$
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