解；由a>1可得a-1>0因为ab-4a-b+1=0(a>1)所以b=（4a-1）/（a-1）设f（a）=(a+1)(b+2）将b=（4a-1）/（a-1）代入可得f(a)=(a+1)(b+2)=(a+1)(（4a-1）/（a-1）+2)=(6a-3)(a+1)/(a-1)=6(a-1)+[6/(a-1)]+15由于a-1>0所以...