101+102+103+...+200??

a = 101
b = U2 - U1 = 102 - 101 = 1
Un = 200

Un = a + (n - 1)b
200 = 101 + (n - 1)1
200 = 101 + n - 1
200 = 100 + n
200 - 100 = n
100 = n

Sn = n/2 (a + Un)
S100 = 100/2 (101 + 200)
S100 = 50 . 301
S100 = 15.050

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