题目

设f(x)是定义在正整数集上的函数,且满足f(x+2)=f(x+1)-f(x),如果f(1)=lg,f(2)=lg15,则f(2 008)的值为(    )A.lg15-1        B.-lg15             C.-1               D.1-lg15 答案：D解析:f(1)=lg15-1,f(2)=lg15,f(3)=f(2)-f(1)=1,f(4)=f(3)-f(2)=1-lg15,f(5)=f(4)-f(3)=-lg15,f(6)=f(5)-f(4)=-1,f(7)=f(6)-f(5)=lg15-1,……可以想象从f(7)开始重复上述数,即f(x+6)=f(x),∴f(2 008)=f(334×6+4)=f(4)=1-lg15.故选D.--Our hometown Hunan is a wonderful place.You __________________A.must come for a visit.???? B.must come? in a visit.???????? C.need come to a visit.