. =   + =   d. ( ) ( ) 2 2 2 2 2 2 log 1 log 3 81 x xy y x y xy − +  + = +   =  (ĐH_Khối A 2009) ĐS: (2;2), (−2;−2) e. ( ) 2 3 9 3 1 2 1 3log 9 log 3 x y x y  − + − =   − =   (ĐH_Khối