Question

Calcule a soma dos n primeiros termos da PA (n-3,n-1...)

Answer 1

r = n - 1 -(n - 3)
r = n - 1 - n + 3
r = 2
an = a1 + (n - 1) r
an = n -1 + (n - 1)2
an = n - 3 + 2n -2
an = 3n - 5
Sn = (a1 + an).n/2
Sn = (n -3 + 3n -5) .n/2
Sn = (4n - 8) . n/2
Sn = (2n - 4)n
Sn = 2(n - 2)n
Sn = 2n(n-2)