Question

Calcule a soma dos 10 primeiros termos da P.A. (3, 7, 11, ...)

resposta com cálculo prfv​​

Answer 1

$\begin{array}{l}r=a_{2} -a_{1} =7-3\Longrightarrow r=4\\\\a_{10} =a_{1} +9r=3+9\cdotp 4\Longrightarrow a_{10} =39\\\\\therefore S_{10} =\frac{( a_{1} +a_{10}) \cdotp 10}{2} =( 3+39) \cdotp 5\\\\\Longrightarrow S_{10} =210\end{array}$