Question

Qual a soma dos trinta primeiros da PA (4,10...)

Answer 1

1° vamos encontrar an

$a_1=4~~~~~~n=30~~~~~~~r=10-4=6 \\ \\ a_n=a_1+(n-1)r \\ \\ a_n=4+(30-1)6 \\ \\ a_n=4+(29)6 \\ \\ a_n=4+174 \\ \\ a_n=178$


vamos calcular a soma

$a_1=4~~~~a_n=178~~~~n=30 \\ \\ S_n= \frac{(a_1+a_n)n}{2} \\ \\ S_n= \frac{(4+178)\not30^{15}}{\not2} \\ \\ S_n=182.15 \\ \\ S_n=2730$