（x的平方-3）的平方-x（x的平方-3）-2x的平方

( x" - 3 )" - x( x" - 3 ) - 2x"
= ( x” - 3 )” - 2x( x" - 3 ) + x( x" - 3 ) - 2x"
= ( x" - 3 )( x" - 2x - 3 ) + x( x" - 2x - 3 )
= ( x" + x - 3 )( x” - 3x + x - 3 )
= ( x" + x - 3 )[ x( x - 3 ) + ( x - 3 ) ]
= ( x“ + x - 3 )( x - 3 )( x + 1 )