Question

calcule a soma 25 primeiros números naturais pares​

Answer 1

$a_1=2$
$a_n=24$

$a_n=a_1+(n-1)*r$
24=2+(n-1)*2
24=2+2n-2
2n=24
n=24/2
n=12

$sn=(a_1+a_n)*n/2$
s12=(2+24)*12/2
s12=(26*12)2
s12=312/2
s12=156