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1 the tenth term of an arithmetic series is 67 and the sum o

学习 时间:2026-03-30 12:36:41 阅读：6475
1 the tenth term of an arithmetic series is 67 and the sum of the first twenty terms is 1280.find the common difference ,d and the first term a .2 if the first term of an arithmetic sequence is 3 and the hundredth tern is 307,then find the sum of the first 100 terms.3 an arithmetic sequence has thirteen terms whose sum is 143.the third term is 5.find the first term.
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爱撒娇的鸡

神勇的向日葵

2026-03-30 12:36:41

a10=67,s20=1280 20*(a1+a20)/2=1280-->a1+a20=a1+a1+19d=128 a10=(a1+a19)/2=67 --> (128-d)/2=67 -->d=-6 a=1212。a1=3 a100=307 -->s100=(3+307)*100/2=155003。s13=143 a3=5a1=5-2d a13=5+10d(10+8d)*13/2=143 --> d=1。5a1=2

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  • 文艺的灰狼
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    2026-03-30 12:36:41

    a10=67,s20=1280 20*(a1+a20)/2=1280-->a1+a20=a1+a1+19d=128 a10=(a1+a19)/2=67 --> (128-d)/2=67 -->d=-6 a=1212。a1=3 a100=307 -->s100=(3+307)*100/2=155003。s13=143 a3=5a1=5-2d a13=5+10d(10+8d)*13/2=143 --> d=1。5a1=2

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