y=log2[(x^2-2x+5)/(x-1)]y=log2[(x-1)^2+4)/(x-1)]y=log2[(x-1)+4/(x-1)]所以仅求[(x-1)+4/(x-1)]的值域由均值不等式可知x-1+4/x-1≥4（x=3时取=）,已舍负值域所以y=log2[(x^2-2x+5)/(x-1)]的值域为[2,+∞）...