一元二次方程 x 2 - 4 x + 3 = 0 的解为 ( )
x 1 = - 1 , x 2 = 3
x 1 = 1 , x 2 = 3
x 1 = 1 , x 2 = - 3
x 1 = - 1 , x 2 = - 3
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