Ответы на вопрос:
1. b1•q^2=18 b1•9=18 b1=18/9=2 b1•(q^5–1) 2•242 s5 = = = 242 q–1 2 2a1+49d 2. s50 =•50=(2a1+49•4)•25= 2 = (2a1+196)•25 (2a1+196)•25=5500 |: 25 2a1+196=220 2a1=24 a1=12 2a1+13d 3. s14 = • 14 = (2a1+13d)•7 = 2 = (2•10+13d)•7 = (20+13d)•7 (20+13d)•7 = 1050 |: 7 20+13d = 150 13d = 130 d = 10
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