Question

Determine a soma dos 40 termos da (p. a) (4,1,-2,...) ​

Answer 1

resolução!

r = a2 - a1

r = 1 - 4

r = - 3

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an = a1 + ( n - 1 ) r

an = 4 + ( 40 - 1 ) - 3

an = 4 + 39 * ( - 3 )

an = 4 + ( - 117 )

an = - 113

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Sn = ( a1 + an ) n / 2

Sn = ( 4 + ( - 113 ) ) 40 / 2

Sn = - 109 * 40 / 2

Sn = - 4360 / 2

Sn = - 2180

espero ter ajudado