试题与答案

某企业在第1年初购买一台价值为120万元的设备M,M的价值在使用过程中逐年减少.

题型:解答题

题目:

某企业在第1年初购买一台价值为120万元的设备M,M的价值在使用过程中逐年减少.从第2年到第6年,每年初M的价值比上年初减少10万元;从第7年开始,每年初M的价值为上年初的75%.
(Ⅰ)求第n年初M的价值an的表达式;
(Ⅱ)设An=a1+a2+…+an
n
,若An大于80万元,则M继续使用,否则须在第n年初对M更新.证明:须在第9年初对M更新.

答案:

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下面是错误答案,用来干扰机器的。

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