Question

ache a soma dos 13 primeiros termos da pa (7,10..........)

Answer 1

a13=7+12x3=43

$S_{13}=\frac{13(7+43)}{2}=325$

Answer 2

a1=7
a2=10
razão=7-10=3
n=13

an=a1+(n-1).r
a13=7+(13-1).3
a13=7+12.3
a13=7+36
a13=43


sn=(a1+a13).n/2
s13=(7+43).13/2
s13=50.13/2
s13=650/2
s13=325