用配方法解一元二次方程 x 2 - 4 x + 1 = 0 时,下列变形正确的是 ( )
( x - 2 ) 2 = 1
( x - 2 ) 2 = 5
( x + 2 ) 2 = 3
( x - 2 ) 2 = 3
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