Naydite summu n pervix chlenov arifmeticheskoy progressii: - вопрос №166455391114 от hfhfhjfy 29.04.2021 07:05

Question

Алгебра: Naydite summu n pervix chlenov arifmeticheskoy progressii: 1)a1=-1, an=-40, n=20.

hfhfhjfy · Answer

X(x - 1) + 5y(x - 1) = 7(x - 1) (x + 5y) = 7Существует четыре варианта: 1) x - 1 =7 , x + 5y = 1 , 2) x - 1 = 1 , x + 5y = 7 , 3) x - 1 = - 1,  x + 5y = - 7 , 4) x - 1 = - 7 , x + 5y = - 1     1) x - 1 = 7      x = 8       8 + 5y = 1                     5y = - 7                     y = - 1,42) x - 1 = 1    x = 2         2 + 5y = 7                     5y = 5                     y = 13) x - 1 = - 1         0 + 5y = - 7    x = 0                 5y = - 7                             y = - 1,44) x - 1...