Question

QUAL A SOMA DOS TRINTA PRIMEIROS TERMOS DA PA (-15,-11,-7,3)

Answer 1

$An=A1+(n-1)r$

$r=An-A(n-1) =\ \textgreater \ -11-(-15)=4$

$A30=-15+(30-1)4$ $A30=116-15=\ \textgreater \ 101$

$Sn= \frac{(A1+An)n}{2}$

$S30= \frac{(-15+101)30}{2}=\ \textgreater \ 1290$