計(jì)數(shù)之歸納法練習(xí)四
1.滿足1·2+2·3+3·4+…+n(n+1)=3n2-3n+2的自然數(shù)等于 ( )
A.1;B.1或2;C.1,2,3;D.1,2,3,4;
2.在數(shù)列{an}中, an=1-…則ak+1= ( )
A.ak+;B.ak+ C.ak+.D.ak+.
3.用數(shù)學(xué)歸納法證明"當(dāng)n為正奇數(shù)時(shí),xn+yn能被x+整除"的第二步是 ( )
A.假使n=2k+1時(shí)正確,再推n=2k+3正確; B假使n=2k-時(shí)正確,再推n=2k+1正確;
C. 假使n=k時(shí)正確,再推n=k+1正確;D假使n≤k(k≥1),再推n=k+2時(shí)正確(以上k∈Z)
答案詳解見下頁(yè)