∵a^2+b^2=3ab
∴a²+2ab+b²=5ab,a²-2ab+b²=ab
(a+b)²=5ab,(a-b)²=ab
a+b=√(5ab),a-b=√(ab) (∵a>b>0)

a^2+2ab+b^2/a-2b除以a^2-b^2/a-2b
=(a+b)²/[(a+b)(a-b)]
=(a+b)/(a-b)
=√(5ab)/√(ab)
=√5


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