Question

Свойства арифметической прогресси

Answer 1

$\left \{ {{c _{10} =74} \atop { c_{15} =114}} \right.\\\\ -\left \{ {{ c_{1}+9d=74 } \atop { c_{1}+14d=114 }} \right.$
______________
- 5d = - 40
d = 8
c₁ = 74 - 9d = 74 - 9 * 8 = 74 - 72 = 2
Ответ: c₁ = 2  ;  d = 8