@ @QQQ@ @pý†bɾa@ @ 10 [AHSME 1958] ( ) . 20 2() 1( ) 10 ( ) 1 () 2 10 x2 −x −a = 0 a () x 2 + ax + 1 = 0 3 ( ) 2 ( ) 1 ( ) −1( )