(1) ∵x>1 ,x-1>0
x + 9/(x-1) =(x-1) + 9/(x-1) +1
≥2√[(x-1)*9/(x-1)] +1 =7
当且仅当x-1=9/(x-1)即x=4时取等号
即x + 9/(x-1)最小值是7.
(2) ∵x