1.
a1 = 15
a2 = 20
r = a2 - a1 = 20 - 15 = 5
an = a1 + (n - 1) * r
an = 15 + (n - 1) * 5
an = 15 + 5n - 5
an = 10 + 5n
2.
dany ciąg to: 52, 47, ....(-53)
a1 = 52
a2 = 47
an = -53
r = a2 - a1 = 47 - 52 = -5
-53 = 52 + (n - 1) * (-5)
-53 - 52 = -5n + 5
-105 - 5 = -5n
-110 = -5n
n = 22
Sn = (a1 + an) * n) / 2
Sn = (52 + (-53)) * 22) / 2
Sn = = (-1) * 11
Sn = -11
W załączniku :)
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1.
a1 = 15
a2 = 20
r = a2 - a1 = 20 - 15 = 5
an = a1 + (n - 1) * r
an = 15 + (n - 1) * 5
an = 15 + 5n - 5
an = 10 + 5n
2.
dany ciąg to: 52, 47, ....(-53)
a1 = 52
a2 = 47
an = -53
r = a2 - a1 = 47 - 52 = -5
an = a1 + (n - 1) * r
-53 = 52 + (n - 1) * (-5)
-53 - 52 = -5n + 5
-105 - 5 = -5n
-110 = -5n
n = 22
Sn = (a1 + an) * n) / 2
Sn = (52 + (-53)) * 22) / 2
Sn = = (-1) * 11
Sn = -11
W załączniku :)