Respostas

2014-03-05T17:52:07-03:00
PA (-7, -27/4, -13/2, -25/4, ....) => Sn = n (a + a₁₈)/2, e an = a₁ + (n-1)r
n = 18
a
 = -7
r = a
 - a = a - a = a - a = 1/4, logo:
a
₁₈ = -7 + (17. 14) = -11/4 
S
₁₈ = 18 (-7 - 11/4)2 = 9(-39/4) = -351/4


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