x²-5x-1=0x²-1=5x∴ x-1/x=5∴ (x-1/x)²=25∴ x²+1/x²-2=25∴ x²+1/x²=27∴ x²+1/x²-11=16∴ 根号（x²+1/x²-11）=根号16=4