7-9x-4x+5 = 2-3x => 12-13x = 2-3x=> 13x-3x = 12-2 => 10x=10 =>x=1
两边乘以x^2-4 => (x-2)^2 -x^2 +4 = 16 => -4x = 8 => x=-2
分子 (a-1) * ( a-2) * ( a+2)
分母: (a-2)^2 * (a-1)* (a+1)
约分后,得到(a+2)/(a-2)(a+1)
(a^2 -(a+1)(a-1))/(a-1) = 1/(a-1)
懒得浪费时间,正在写另一个试卷,现在的试卷,哎