H
hoaseru


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[QUOTE][IMG]http://bjhj[/IMG][/QUOTE]
u1=u2=1va` un=2u(n-2)+u(n=1),n\geq3
chung minh rang: moi so hang cua day~ so deu la cap so cong.sao to danh tieng viet no khong ra nhi? may no' bi mac o cho~ nao`? chi? cho to voi'.