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【319499】【详解】三年级(上)第21讲 等差数列求和

时间:2025-01-07 22:54:22 作者: 字数:1397字
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第二十一讲 等差数列求和

  1. 例题1
    答案:(1165;(2231
    详解:1 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>
    2 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  2. 例题2
    答案:(1616;(2712
    详解:1)先求项数= <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,再求和: <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>
    2先求项数= <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>  <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  3. 例题3
    答案:(1390;(22041
    详解:1)先求末项= <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>  <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>
    2)先求末项= <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>  <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  4. 例题4
    答案:(18天;(2204
    详解:先求项数,即多少天= <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> 天, <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,即共有204页.

  5. 例题5
    答案:360
    详解:利用中间数×项数,共有 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> 颗.

  6. 例题6
    答案:63
    详解: <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,则多加的数为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,则漏加的数为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,则被重复计算和漏掉的两数之和为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  7. 练习1
    答案:234
    简答: <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  8. 练习2
    答案:672
    简答:先求项数= <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>  <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  9. 练习3
    答案:318
    简答:先求末项= <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>  <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  10. 练习4
    答案:3600
    简答:先求项数,有 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> 天, <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,即共游了3600米.

  11. 作业1
    答案:476
    简答:首项为70,末项为49,项数为8 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  12. 作业2
    答案:791
    简答:项数为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,和为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  13. 作业3
    答案:1550
    简答:末项为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,和为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  14. 作业4
    答案:800
    简答:公差为2,第20项为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a> ,和为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

  15. 作业5
    答案:162
    简答:前9项的中间项是第5项.所以前9项和为 <a href="/tags/120/" title="求和" class="c1" target="_blank">求和</a> <a href="/tags/221/" title="等差数列" class="c1" target="_blank">等差数列</a> <a href="/tags/162/" title="数列" class="c1" target="_blank">数列</a>

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