f(x)=[x^2-2(a-1)x+(a-1)^2]+1-(a-1)^2=[x-(a-1)]^2+1-(a-1)^2 （先凑完全平方式）该函数的抛物线开口向上,f(x)在[x-(a-1)]＝0时有最小值,已知f(x)在[2,正无穷大）上是增函数,x=2时f(x)取得最小值综上所述：x=2时,[x...