Question

o termo geral de uma p.a é an=48-5n,n calcule a soma de seus 10 primeiros termos

Answer 1

$a_n=48-5n\\\\\\\begin{matrix}a_1&=&48-5(1)\\\\a_{1}&=&48-5\\\\a_1&=&43\end{matrix}\qquad\qquad\qquad\qquad\qquad\begin{matrix}a_{10}&=&48-5(10)\\\\a_{10}&=&48-50\\\\a_{10}&=&-2\end{matrix}\\\\\\\\S_n=\dfrac{n(a_1+a_n)}{2}\\\\\\S_{10}=\dfrac{10(43+(-2)))}{2}\\\\\\S_{10}=\dfrac{10(41))}{2}\\\\\\S_{10}=5(41)\\\\\boxed{S_{10}=205}$