已知x=根号5-2分之根号5-2,y=根号5+2分之根号5-2.求（1）x+y （2）xy （3）x+y分之x²

x=(√5+2)/(√5-2)
=(√5+2)²/[(√5-2)(√5+2)]
=(9+4√5)/(5-2)
=(9+4√5)/3

y=(√5-2)/(√5+2)
=(√5-2)²/[(√5-2)(√5+2)]
=(9-4√5)/(5-2)
=(9-4√5)/3
(1)
x+y=(9+4√5)/3+(9-4√5)/3
=(9+9)/3
=6

(2)
xy=(√5+2)/(√5-2)*(√5-2)/(√5+2)=1
(3)
(x²+3xy+y²)/(x+y)
=[(x+y)²+xy]/(x+y)
=(6²+1)/6
=37/6
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再问： x， （√5-2）（√5+2)怎么是（5-2）
再答： x=(√5+2)/(√5-2) =(√5+2)²/[(√5-2)(√5+2)] =(9+4√5)/(5-4) =9+4√5 y=(√5-2)/(√5+2) =(√5-2)²/[(√5-2)(√5+2)] =(9-4√5)/(5-4) =9-4√5 (1) x+y=(9+4√5)+(9-4√5) =9+9 =18 (3) (x²+3xy+y²)/(x+y) =[(x+y)²+xy]/(x+y) =(18²+1)/18 =325/18