y=x+1/x,(x>0)
å½æ°å¨(0,1)ä¸åè°åï¼å¨(1,+â)ä¸åè°å¢ã
è¯æå¦ä¸ï¼ä»»åx1,x2â(0,1)ï¼ä¸x1<x2
åf(x1)-f(x2)=x1+1/x1-x2-1/x2
=(x1-x2)+1/x1-1/x2
=(x1-x2)+(x2-x1)/(x1x2)
=(x1-x2)(1-1/(x1x2))
å 为0<x1<x2<1
æ以x1-x2<0
0<x1x2<1
æ以1/(x1x2)>1
æ以1-1/(x1x2)<0
æ以(x1-x2)(1-1/(x1x2))>0
å³f(x1)>f(x2)
æ以f(x)å¨(0,1)ä¸æ¯åå½æ°ï¼
åçå¯è¯f(x)å¨(1,+â)ä¸æ¯å¢å½æ°ã
å½æ°å¾åå¦ä¸ï¼