xx
xx<5/4 ===>5-4x>0y=4x-2+1/(4x-5) =4x-5+1/(4x-5)+3 =-[5-4x+1/(5-4x)]+35-4x+1/(5-4x)>=2√(5-4x)*1/(5-4x2)=2 (当且仅当5-4x=1/(5-4x)取到等号)ymax=-2+3=1