Question

calcule a soma dos termos de cada PA. a(3,-1,-5,...,-33)

Answer 1

r = a2 - a1

r = - 1 - 3

r = - 4




an = a1 + ( n - 1 ) r

- 33 = 3 + ( n - 1 ) - 4

- 33 = 3 + ( - 4n ) 4

- 33 = 7 + ( - 4n )

- 33 - 7 = - 4n

- 40 = - 4n * (-1)

40 = 4n

n = 40/4

n = 10

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Sn = ( a1 + an ) n / 2

Sn = ( 3 + ( - 33 ) ) 10 / 2

Sn = - 30 * 10 / 2

Sn = - 300 / 2

Sn = - 150