Question

calcule o décimo terceiro termo da P.A. (4,7,...)

Answer 1

Utilize a  fórmula do termo geral de uma PA:

$a_n=a_1+(n-1)r\\ \\ a_{13}=4+3(13-1)\\ \\ a_{13}=4+36\\ \\ a_13}=40$

Answer 2

$\Large\boxed{\begin{array}{l}\sf a_n=a_1+(n-1)\cdot r\\\sf a_{13}=4+(13-1)\cdot 3\\\sf a_{13}=4+12\cdot3\\\sf a_{13}=4+36\\\sf a_{13}= 40~\checkmark\end{array}}$