已知m>4,化简:|m-4|+|7-2m|+|m^2-2m+1|-|m^2-2m-3|

∵m>4
∴m-4>0,7-2m0,m+1>0,m-3>0
∴(m+1)(m-3)>0
∴原式=|m-4|+|7-2m|+|(m-1)²|-|(m+1)(m-3)|
=m-4+2m-7+(m-1)²-(m+1)(m-3)
=3m-11+m²-2m+1-m²+2m+3
=3m-7