Дано а1=10 n=11 Sn=330 найти an и d

Question

Дано а1=10 n=11 Sn=330 найти an и d

Answer 1

Sn = (2a1 + d(n-1) / 2) * n
330 = (2 * 10 + 10d / 2) * 11
30 = 20 + 10d / 2
60 = 20 + 10d
d = 40 / 10 = 4
an = a1 + (n-1)d = 10 + 10 * 4 = 50