2x" - 4x + 5
= 2x" - 4x + 2 + 3
= 2[ ( x - 1 )" + 3/2 ]
= 2[ ( x - 1 )" - ( -6/4 ) ]
= 2{ ( x - 1 )" - [ (√6/ 2)i ]" }
= 2[ x - 1 - (√6/ 2)i ][ x - 1 + (√6/ 2)i ]
或者
= 2[ 2x /2 - 2/2 - (√6/ 2)i ][ 2x /2 - 2/2 + (√6/ 2)i ]
= (1/2)( 2x - 2 - √6i )( 2x - 2 + √6i )