Question

Numa progressão aritmética a10 = -3 e a12 = 11. Determine o valor de a5

 

Answer 1

$<var>a_{11}=\frac{a_{12}+a_{10}}{2}(termo.medio)\\\\a_{11}=\frac{11+(-3)}{2}=>a_{11}=4\\\\r=a_{12}-a_{11}=>r=11-4=>r=7\\\\a_{j}=a_{i}+(j-i).r(termo.geral)\\\\a_{12}=a_{5}+(12-5).r\\11=a_{5}+(7).7=>a_{5}=11-49=-38\\\\a_{5}=-38</var>$