a+1分之2a+1+a-1分之a-4
=a+1分之(2a+2-1)+a-1分之(a-1-3)
=2-(a+1)分之1+1-(a-1)分之3
=3-【(a+1)分之1+(a-1)分之3】
=3-(a+1)(a-1)分之(a-1+3a+3)
=3-(a+1)(a-1)分之(4a+2)
a+1分之2a+1+a-1分之a-4
=a+1分之(2a+2-1)+a-1分之(a-1-3)
=2-(a+1)分之1+1-(a-1)分之3
=3-【(a+1)分之1+(a-1)分之3】
=3-(a+1)(a-1)分之(a-1+3a+3)
=3-(a+1)(a-1)分之(4a+2)