先化简,再求值: ( x + 1 x - 2 - 1 ) ÷ x 2 - 2 x x 2 - 4 x + 4 ,其中 x = 3 .
化简: ( a a - 1 + 5 a + 9 a 2 - 1 ) ÷ a + 3 a - 1 .
化简: ( a + 2 a 2 - 2 a - a - 1 a 2 - 4 a + 4 ) ÷ a - 4 a .