Question

dada a P.A (13,15,17,19,...55)encontre a soma de seus termos​

Answer 1

r= a2-a1

r=15-13

r= 2

an= A1+(n-1).r

55=13+(n-1).2

55= 13+2n-2

55=11+2n

55-11= 2n

44= 2n

n= 44/2

n= 22

Sn= (A1+an).n

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_______2

Sn= (13+55).22

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_________2

Sn= 68.22

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_______2

Sn= 1496/2

Sn=748