Question

´RECISO DA CONTA PFV!! A soma dos termos dessa P.A.( – 22, – 18, – 14, .... , 82 ) é:

Answer 1

$\large\boxed{\begin{array}{l}\sf a_n=a_1+(n-1)\cdot r\\\sf 82=-22+(n-1)\cdot4\\\sf -22+4n-4=82\\\sf 4n=82+22+4\\\sf 4n=108\\\sf n=\dfrac{108}{4}\\\sf n=27\\\sf S_n=\dfrac{n\cdot(a_1+a_n)}{2}\\\sf S_{27}=\dfrac{27\cdot(-22+82)}{2}\\\sf S_{27}=\dfrac{27\cdot\diagdown\!\!\!\!\!\!60^{30}}{\diagdown\!\!\!2}\\\sf S_{27}=27\cdot30\\\sf S_{27}=810\end{array}}$