pomocy sztbko !
wiedząc ze ciag jest arytmetyczny i mając dane : a1=1 , r=2, n=20 znajdz an i sn
szybko pomocy
an = a1 + (n - 1) * r
an = 1 + (20 - 1) * 2
an = 1 + 38
an = 39
Sn = (a1 + an) / 2 * n = (1 + 39) / 2 * 20 = 400
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an = a1 + (n - 1) * r
an = 1 + (20 - 1) * 2
an = 1 + 38
an = 39
Sn = (a1 + an) / 2 * n = (1 + 39) / 2 * 20 = 400