Объяснение:
a₁ = 6, d = - 2
S ₃₀ = ( 2 a₁ + 29d) * n / 2 = (2 * 6 + (-2) * 29 ) * 30 / 2 = (12-58) * 15 = -46 * 15 = - 690
S₃₀ = - 690
Объяснение:
a₁ = 6, d = - 2
S ₃₀ = ( 2 a₁ + 29d) * n / 2 = (2 * 6 + (-2) * 29 ) * 30 / 2 = (12-58) * 15 = -46 * 15 = - 690
S₃₀ = - 690