Question

Achar a soma dos 60 primeiros termos da p.a.(2,5,...)

Answer 1

An=a1+(n-1).r
An=2+(60-1).3
An=2+59.3
An=2+177
An=179
======================
Sn=(a1+an).n/2
Sn=(2+179).60/2
Sn=181.60/2
Sn=10.860/2
Sn=5.430 ///

Answer 2

$a_{1} =2$

$r=5-2=3$

$a_{n} =a_{1} +(n-1).r$

$a_{60} =2 +59.3=179$

$S_{n} = \frac{( a_{1} +a_{n}).n}{2}$

$S_{60} = \frac{(2+179).60}{2} = 181.30=5430$