Question

Determine: A) a soma dar 10 primeiros termos da p.a (2,5,...)

Answer 1

d=5-2=3

an=a1+(n-1)d
an=2+(n-1)3
an=2+3n-3
an=3n-1

a10=3*10-1
a10=30-1
a10=29

sn=(a1+an)n/2
s10=(2+29)10/2
s10=31*5
s10=155