Question

Calcular a soma dos termos da P.A ( -16,-14,-12.....,84).

Answer 1

resolução!

r = a2 - a1

r = - 14 - ( - 16 )

r = 2

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an = a1 + ( n - 1 ) r

84 = - 16 + ( n - 1 ) 2

84 = - 16 + 2n - 2

84 = - 18 + 2n

84 + 18 = 2n

102 = 2n

n = 102/2

n = 51

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Sn = ( a1 + an ) n / 2

Sn = ( - 16 + 84 ) 51 / 2

Sn = 68 * 51 / 2

Sn = 3468 / 2

Sn = 1734