题目内容
(12分)在德国不来梅举行的第48届世乒赛期间,某商场橱窗里用同样的乒乓球堆成若干堆“正三棱锥”形展品,其中第一堆只有一层,就一个球,第2、3、4、…堆最底层(第一层)分别按下图方式固定摆放,从第二层开始每层的小球自然垒放在下一层之上,第
堆的第
层就放一个乒乓球,以
表示第
堆的乒乓球总数.
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(1)求
;
(2)求
(用
表示)(可能用到的公式:
)
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(1)求
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(2)求
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(1)
=10
(2)
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(2)
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通过观察可知f(3)=10.
(2)在求f(n)时,可以观察归纳出f(n)的递推关系
,
然后再采用叠加求通项的方法求出
.
(2)在求f(n)时,可以观察归纳出f(n)的递推关系
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然后再采用叠加求通项的方法求出
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