若(x+1/x)^2=9,则(x-1/x)^2=_______;已知x^2+y^2=6,xy=5,则x+y=_______.

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若(x+1/x)^2=9,则(x-1/x)^2=_______;已知x^2+y^2=6,xy=5,则x+y=_______.

(x+1/x)^2=9,
则(x-1/x)^2
=x²-2+1/x²
=x²+2+1/x²-4
=(x+1/x)²-4
=9²-4
=77
x^2+y^2=6,xy=5
∴(x+y)²=x²+y²+2xy=6+10=16
∴x+y=±4