Question

Calcule a soma de Pá (2,7,12,17,22,27)

Answer 1

a1 = 2 
r = 7-2 = 5 

an = a1+(n-1).r 
an = 2+(n-1).5 
an = 2+5n-5 
an = 5n-3 

Sn = (a1+an).n/2 
Sn = (2+5n-3).n/2 
Sn = (5n-1).n/2 
ou 
Sn = (5n²-n)/2

Answer 2

Calcule a soma de Pá (2,7,12,17,22,27)

a1 = 2
r = 7-2 = 5
an = 27

2 + ( n-1).5 = 27

5n - 5  +  2 = 27

5n = 27+3 ==> 5n ==> 30 ==> n = 6
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Sn = (a1+an).n
              2

S6 = (2+27).6
            2

S6 = 29.3 ==> S6 = 87