Question

Numa P.A cuja 2 termo e igual a 5 e o 6 termo e igual a 13 o 20 termo igual a :

Answer 1

$\large\boxed{\begin{array}{l}\tt dados \begin{cases}\sf a_2=5\\\sf a_6=13\\\sf a_{20}=?\end{cases}\\\underline{\boldsymbol{soluc_{\!\!,}\tilde ao\!:}}\\\sf a_6=a_2+4r\\\sf 13=5+4r\\\sf 4r=13-5\\\sf 4r=8\\\sf r=\dfrac{8}{4}\\\\\sf r=2\\\sf a_{20}=a_6+14r\\\sf a_{20}=13+14\cdot2\\\sf a_{20}=13+28\\\sf a_{20}=41\end{array}}$