Question

progresia arimetrica????dau coroana

Answer 1

$a_3=a_1+2r=11$

$a_8=a_1+7r=31$

$a_1+2r=11$

$a_1+2r=11$

$a_1+7r=31$

$-5r=-2 / :(-5)$

$r=4$

$a_1+8=11$

$a_1=3$

$a_{26}=3 + (26-1) \cdot 4$

$a_{26}=3 + 25 \cdot 4$

$a_{26}=106$

Answer 2

Răspuns:

103

Explicație pas cu pas:

$\begin{cases}a_{3} = a_{1} + 2 \cdot r \\a_{8} = a_{1} + 7 \cdot r \end{cases} \iff \begin{cases}a_{1} + 2 \cdot r = 11\\a_{1} + 7 \cdot r = 31\end{cases}$

$7r - 2r = 31 - 11 \\ 5r = 20 \implies r = 4$

$a_{1} + 2 \cdot 4 = 11 \\ a_{1} = 11 - 8 \implies a_{1} = 3$

$a_{26} = a_{1} + 25 \cdot r = 3 + 25 \cdot 4 = 3 + 100 = \bf 103$