Ответ:
S = 114
Объяснение:
S = (a₁ + aₙ)/2 * n
aₙ = a₁ + (n-1)*d
a₁₂ = 7 + (11 * (-3)) = -26
S = (7 -26)/2 * 12 = 114
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Ответ:
S = 114
Объяснение:
S = (a₁ + aₙ)/2 * n
aₙ = a₁ + (n-1)*d
a₁₂ = 7 + (11 * (-3)) = -26
S = (7 -26)/2 * 12 = 114