三名篮球运动员甲,乙,丙进行传球训练,由甲开始传,经过6次传递后,球又被传回给甲,则不同的传球方式
\u4e09\u540d\u7bee\u7403\u8fd0\u52a8\u5458\u7532\uff0c\u4e59\uff0c\u4e19\u8fdb\u884c\u4f20\u7403\u8bad\u7ec3\uff0c\u7531\u7532\u5f00\u59cb\u4f20\uff0c\u7ecf\u8fc76\u6b21\u4f20\u9012\u540e\uff0c\u7403\u53c8\u88ab\u4f20\u56de\u7ed9\u7532\uff0c\u5219\u4e0d\u540c\u7684\u4f20\u7403\u65b9\u5f0f\u6839\u636e\u9898\u610f\uff0c\u8bbe\u5728\u7b2cn\u6b21\u4f20\u7403\u540e\uff08n\u22652\uff09\uff0c\u6709a n \u79cd\u60c5\u51b5\u7403\u5728\u7532\u624b\u4e2d\uff0c\u5373\u7ecf\u8fc7n\u6b21\u4f20\u9012\u540e\uff0c\u7403\u53c8\u88ab\u4f20\u56de\u7ed9\u7532\uff0c\u800c\u524dn\u6b21\u4f20\u7403\u4e2d\uff0c\u6bcf\u6b21\u4f20\u7403\u90fd\u67092\u79cd\u65b9\u6cd5\uff0c\u5219\u524dn\u6b21\u4f20\u7403\u7684\u4e0d\u540c\u7684\u4f20\u7403\u65b9\u6cd5\u5171\u67092 n \u79cd\uff0c\u90a3\u4e48\u5728\u7b2cn\u6b21\u4f20\u7403\u540e\uff0c\u7403\u4e0d\u5728\u7532\u624b\u4e2d\u7684\u60c5\u51b5\u67092 n -a n \u79cd\u60c5\u51b5\uff0c\u5373\u7403\u5728\u4e59\u6216\u4e19\u624b\u4e2d\uff0c\u53ea\u6709\u5728\u8fd9\u4e9b\u60c5\u51b5\u65f6\uff0c\u5728\u7b2cn+1\u6b21\u4f20\u7403\u540e\uff0c\u7403\u624d\u4f1a\u88ab\u4f20\u56de\u7532\uff0c\u5373a n+1 =2 n -a n \uff1b\u6613\u5f97a 2 =2\uff0c\u5219a 3 =2 2 -2=2\uff0ca 4 =2 3 -2=6\uff0ca 5 =2 4 -6=10\uff0ca 6 =2 5 -10=22\uff0c\u6545\u9009D\uff0e
http://v.youku.com/v_playlist/f1895882o1p4.html
\u8fd9\u4e2a\u662f \u5f20\u536b\u5e73\u7684\u89c6\u9891
\u6211\u521d\u4e2d\u65f6\u5c31\u662f\u770b\u8fd9\u4e2a\u7ec3\u7684
\u5f88\u4e0d\u9519 \u975e\u5e38\u6709\u5e2e\u52a9
而前n次传球中,每次传球都有2种方法,则前n次传球的不同的传球方法共有2n种,
那么在第n次传球后,球不在甲手中的情况有2n-an种情况,即球在乙或丙手中,
只有在这些情况时,在第n+1次传球后,球才会被传回甲,即an+1=2n-an;
易得a2=2,则a3=22-2=2,a4=23-2=6,a5=24-6=10,a6=25-10=22,
故选D.
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