Найдите сумму первых 17-ти членов арифсетической прогрессии,если известно,что a7+a11=20 - №32565446

Найдите сумму первых 17-ти членов арифсетической прогрессии,если известно,что a7+a11=20
- Предмет:
  Математика
- Автор:
  alfieuesm
- 5 лет назад

Ответы 1

S17= (2a1+16d)/2*17
a1+6d+a1+10d=20
2a1+16d=20
S17=20/2*17= 10*17= 170
- Автор:
  darwin45
- 5 лет назад
- 0
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