∵a²+b²-6ab=0∴(a-b)²=4ab (a+b)²=8ab∵a>b>0∴a-b>0，a+b>0∴a-b=2√(ab)，a+b=2√2√(ab)∴(a+b)/(b-a)=-(a+b)/(a-b)=-2√(ab)/[2√2√(ab)]=-1/√2=-√2
