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一元二次方程 x 2 - 4 x - 1 = 0 配方后可化为 ( )
( x + 2 ) 2 = 3
( x + 2 ) 2 = 5
( x - 2 ) 2 = 3
( x - 2 ) 2 = 5
解方程: x 2 - 2 x = 4 .
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