已知数列{xn}满足xn+1=xn-xn-1(n≥2),x1=a,x2=b,记Sn=x1+x2+…+xn.则下列结论正确的是(A) x100= -a ,S100=2b-a;(B) x100= -b ,S100=2b-a;(C) x100= -b ,S100=b-a;(D) x100=-a ,S100=b-a;
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已知数列{xn}满足xn+1=xn-xn-1(n≥2),x1=a,x2=b,记Sn=x1+x2+…+xn.则下列结论正确的是(A) x100= -a ,S100=2b-a;(B) x100= -b ,S100=2b-a;(C) x100= -b ,S100=b-a;(D) x100=-a ,S100=b-a;
已知数列{xn}满足xn+1=xn-xn-1(n≥2),x1=a,x2=b,记Sn=x1+x2+…+xn.则下列结论正确的是
(A) x100= -a ,S100=2b-a;
(B) x100= -b ,S100=2b-a;
(C) x100= -b ,S100=b-a;
(D) x100=-a ,S100=b-a;
已知数列{xn}满足xn+1=xn-xn-1(n≥2),x1=a,x2=b,记Sn=x1+x2+…+xn.则下列结论正确的是(A) x100= -a ,S100=2b-a;(B) x100= -b ,S100=2b-a;(C) x100= -b ,S100=b-a;(D) x100=-a ,S100=b-a;
x1=a
x2=b
x3=x2-x1=b-a
x4=x3-x2=-a
x5=x4-x3=-b
x6=x5-x4=a-b
x7=x6-x5=a
所以这个数列是循环的,100除以6余4所以x100=x4=-a
S6=S12=...=96=0
S100=S96+x97+x98+x99+x100=x1+x2+x3+x4=2b-a
选A,一般这种特别离奇的数列都是循环的,不然就没法做了.
答案是A
你仔细看看就是了
不难啊
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