因式分解 a²-a-2

因式分解 a²-a-2

a" - a - 2
= a" - 2a + a - 2
= a( a - 2 ) + ( a - 2 )
= ( a - 2 )( a + 1 )
或者
= a" + a - 2a - 2
= a( a + 1 ) - 2( a + 1 )
= ( a + 1 )( a - 2 )

=(a+1)(a-2)
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