a9 = a1+8×d = 2+8×(-4) = 2-32 = -30
s9 = (2-30)÷2×9 = -14×9 = -126
Ответ: а9 = -30; s9 = -126
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a9 = a1+8×d = 2+8×(-4) = 2-32 = -30
s9 = (2-30)÷2×9 = -14×9 = -126
Ответ: а9 = -30; s9 = -126