Предмет: Алгебра, автор: angelinasagaldi

Арифметическая прогрессия содержит члены a7=54 и a15=110, найдите a3.
Помогите пожалуйста. С пояснениями плиз:)

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Автор ответа: NNNLLL54
0
a_7=a_1+6d=54\\a_{15}=a_1+14d=110\\a_{15}-a_7=8d=56,; ; d=7\\a_1+6*7=54\\a_1=54-42=12\\a_3=a_1+2d=12+2*7=26
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