Ответ:
Формула n-го члена арифм. прогрессии [tex]a_{n}=a_1+d\, (n-1)[/tex] .
[tex]\left\{\begin{array}{l}a_7+a_{15}=34\\a_{15}+a_{23}=-68\end{array}\right\ \ \left\{\begin{array}{l}a_{15}=34-a_7\\a_{15}=-68-a_{23}\end{array}\right\ \ \left\{\begin{array}{l}a_{15}=34-a_7\\34-a_7=-68-a_{23}\end{array}\right[/tex]
[tex]\left\{\begin{array}{l}a_{15}=34-a_7\\34-(a_1+6d)=-68-(a_1+22d)\end{array}\right\ \ \left\{\begin{array}{l}a_{1}+14d=34-(a_1+6d)\\34-6d=-68-22d\end{array}\right\\\\\\\left\{\begin{array}{l}2a_1=-20d+34\\16d=-102\end{array}\right\ \ \left\{\begin{array}{l}2a_1=161,5\\d=-6,375\end{array}\right\ \ \left\{\begin{array}{l}a_1=80,75\\d=-6,375\end{array}\right\ \[/tex]
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Ответ:
Формула n-го члена арифм. прогрессии [tex]a_{n}=a_1+d\, (n-1)[/tex] .
[tex]\left\{\begin{array}{l}a_7+a_{15}=34\\a_{15}+a_{23}=-68\end{array}\right\ \ \left\{\begin{array}{l}a_{15}=34-a_7\\a_{15}=-68-a_{23}\end{array}\right\ \ \left\{\begin{array}{l}a_{15}=34-a_7\\34-a_7=-68-a_{23}\end{array}\right[/tex]
[tex]\left\{\begin{array}{l}a_{15}=34-a_7\\34-(a_1+6d)=-68-(a_1+22d)\end{array}\right\ \ \left\{\begin{array}{l}a_{1}+14d=34-(a_1+6d)\\34-6d=-68-22d\end{array}\right\\\\\\\left\{\begin{array}{l}2a_1=-20d+34\\16d=-102\end{array}\right\ \ \left\{\begin{array}{l}2a_1=161,5\\d=-6,375\end{array}\right\ \ \left\{\begin{array}{l}a_1=80,75\\d=-6,375\end{array}\right\ \[/tex]