Question

Determine a soma dos termos de cada PA: (25/6,4,23/6,...,1)​

Answer 1

an=a1+(n-1)r

1=25/6+(n-1)(4-25/6)

1=25/6+(n-1)(-1/6)

1=25/6-1/6n+1/6

-1/6n=1-26/6

-1/6n=-20/6

n=-20/6/-1/6

n=-20/6×-6

n=-20/6

n=20 termos

Aí fazemos a soma dos termos

Sn=(25/6+1)20÷2

Sn=(31/6)x20÷2
Sn=620/6÷2
Sn=620/12
Sn=155/3