Respostas

2013-09-04T10:26:13-03:00
1) P.A (an = ?; a1 = 1; n = 50; r = 2;)
an = a1 + (n -1) . r
an = 1 + (50 -1) . 2
an  1 + 49 . 2 
an = 1 + 98
an = 99

2) an = a1 + (n - 1) . r
    157 = 5 + (20 - 1) . r
    157 = 5 + 19 . r
    157 - 5 = 19 . r
    152 = 19 . r
    152/ 19 = r
    r = 8

3) quarto termo??? 

an = a1 + (n -1) . r
an = -6 + (4 -1) . 8
an = -6 + 3 .8
an = -6 + 24
an = 18

Abraços e espero ter ajudado...
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