Question

calcule a soma dos 50 primeiros termos da PA

a) (-5, -1, 3 ...)

b) (12,5, -2 ...)

c (-7, 3, 13, ...)

Answer 1

Explicação passo-a-passo:

a) (-5, -1, 3 ...)

An=a1+(an-1)*r

A50=-5+(50-1)*4

A50=-5+49*4

A50=-5+196

A50=191

Sn=(a1+an)*n/2

S50=(-5+191)*50/2

S50=186*25

S50=>4650

***********************

b) (12,5, -2 ...)

An=a1+(an-1)*r

A50=12+(50-1)*-7

A50=12+49*-7

A50=12-343

A50=-331

Sn=(a1+an)*n/2

S50=(12-331)*50/2

S50=-319*25

S50=>-7975

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c (-7, 3, 13, ...)

An=a1+(an-1)*r

A50=-7+(50-1)*10

A50=-7+49*10

A50=-7+490

A50=483

Sn=(a1+an)*n/2

S50=(-7+483)*50/2

S50=476*25

S50=>11.900