1. 填空:( 1 ) 3x- ( -2x ) = ;( 3 ) -4xy- ( -2xy ) = ;22223xx( );6xy5x2x2. 计算:232323(1)2( 4)( 3)x yx yx y ;22(2)(35)(47)xxxx ;2(3 7)(1 1)54xx2429xx23(243)x y23x y解:解:22(8 5 6)34xyyx22334xyyx22(3)(83)52(32)xyyxyxyx;解:3. 先化简,再求值:2222221(1)2(2)(2)33abbaabab,其中,;22222222221393abbaa - bbab解:原式 把,带入得,原式22221(2)5(3)(3)1.2x yxyxyx yxy,其中,22222215531261162x yxyxyx yx yxyxy=-解:原式 把,带入得,原式