(2a+1)/(4a-1)-(a+1)/(1-4a)+(5a-4)/(4a-1)
=(2a+1)/(4a-1)+(a+1)/(4a-1)+(5a-4)/(4a-1)
=（2a+1+a+1+5a-4）/(4a-1)
=(8a-2)/(4a-1)
=2
如追加其它问题,