Oblicz sumę k wyrazów ciągu arytmetycznego a, 2a-b, 3a-2b, ...
Poproszę z obliczeniami
a, 2a-b, 3a-2b, ...
r = a2 - a1 = 2a - b - a = a - b
a1 = a
an = a1 +(n - 1) * r
an = a + (n - 1) * (a - b)
Sk = k * (a1 +an) / 2 = k * (a + a + (k - 1)(a - b))/ 2 = 1/2k * [2a + (k - 1)(a - b)]
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a, 2a-b, 3a-2b, ...
r = a2 - a1 = 2a - b - a = a - b
a1 = a
an = a1 +(n - 1) * r
an = a + (n - 1) * (a - b)
Sk = k * (a1 +an) / 2 = k * (a + a + (k - 1)(a - b))/ 2 = 1/2k * [2a + (k - 1)(a - b)]