1*3*5+5*7*9+……97*99*101

学习 时间:2026-09-28 19:26:45 阅读:6412
1*3*5+5*7*9+……97*99*101

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潇洒的丝袜

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2026-09-28 19:26:45

待求和式=∑(4n+1)(4n+3)(4n+5),n从0到24。用裂项相消法,(4n+1)(4n+3)(4n+5) = 1/8 *[(4n+1)(4n+3)(4n+5)(4n+7) - (4n-1)(4n+1)(4n+3)(4n+5)]所以∑(4n+1)(4n+3)(4n+5),n从0到24=1/8 * [97*99*101*103 - (-1)*1*3*5]=1/8 *[999* 10^5 + 24]=12487503

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  • 温柔的花瓣
    回复
    2026-09-28 19:26:45

    待求和式=∑(4n+1)(4n+3)(4n+5),n从0到24。用裂项相消法,(4n+1)(4n+3)(4n+5) = 1/8 *[(4n+1)(4n+3)(4n+5)(4n+7) - (4n-1)(4n+1)(4n+3)(4n+5)]所以∑(4n+1)(4n+3)(4n+5),n从0到24=1/8 * [97*99*101*103 - (-1)*1*3*5]=1/8 *[999* 10^5 + 24]=12487503

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