Дано:арифметическая прогрессияа5=3а7=9Найти S8 - №6487294

Дано:арифметическая прогрессия
а5=3
а7=9
Найти S8
- Предмет:
  Алгебра
- Автор:
  einsteinqibh
- 5 лет назад

Ответы 1

1)a6=(a5+a7)/2
a6=(3+9)/2=6
2) d= 9-6 = 3
3) a8=a7+d
a8=9+3=12
4) a5= a1 + 4d
a1= a5- 4d
a1= 3 - 4* 3=-9
5) s8=((a1+a8)*8)/2
s8=((-9+12)*8)/2=3*8/2=12
Ответ: 12
- Автор:
  kolbybtmx
- 5 лет назад
- 0
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Lisa's First Visit to the Bolshoi Theatre
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