(a+b)²=a²+b²+2ab=5ab(a-b)²=a²+b²-2ab=ab∴(a+b)²/(a-b)²=5ab/ab=5∵a>b∴a+b>0,a-b>0,即(a+b)/(a-b)>0∴(a+b)/(a-b)=√5
