Odpowiedzi

2009-11-06T14:02:37+01:00
An = 1,5,9...
r = 4
a1 = 1
a20 = a1 + 19r
a20 = 1 + 76 = 77
n = 20

Sn = [(a1+a2)/2]*n
sn = [(1+77)/2]*20
Sn = 39 * 20 = 780
3 5 3