Question

calcule a soma dos termos da p.a (-8, -1, -6.... 41)

Answer 1

$\large\boxed{\begin{array}{l}\underline{\rm Soma\,dos\,termos\,da\,PA}\\\sf S_n=\dfrac{n\cdot(a_1+a_n)}{2}\\\\\sf a_n=a_1+(n-1)\cdot r\longrightarrow n=\dfrac{a_n-a_1}{r}+1\\\\\sf n=\dfrac{41-(-8)}{7}+1\\\\\sf n=\dfrac{41+8}{7}+1\\\\\sf n=\dfrac{49}{7}+1=7+1=8\end{array}}$

$\large\boxed{\begin{array}{l}\sf S_8=\dfrac{\backslash\!\!\!8\cdot(-8+41)}{\backslash\!\!\!2}\\\\\sf S_8=4\cdot33=132\end{array}}$