Предмет: Алгебра, автор: Sowira29091999

знайдіть перший член арифметичноі прогресии, якщо а4=11, а20=43

Ответы

Автор ответа: hote

1

$\displaystyle a_4=a_1+3d=11\\\\a_{20}=a_1+19d=43\\\\a_{20}-a_{4}=a_1+19d-a_1-3d=43-11\\\\16d=32\\\\ d=2\\\\a_1=11-3d=11-3*2=11-6=5$

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