1,1+2,2+3,3+...+9,9=???

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вопрос

The pattern in this sequence is that each term is the sum of two consecutive natural numbers. So the sequence can be written as:

1, 3, 5, 7, 9, 11, 13, 15, 17, 19

To find the sum of this sequence, we can use the formula for the sum of an arithmetic series:

S = n/2 * (first term + last term)

where n is the number of terms in the sequence.

In this case, n = 10 and the first term is 1, the last term is 19. Plugging in these values, we get:

S = 10/2 (1 + 19)
S = 5 20
S = 100

Therefore, the sum of the sequence 1+3+5+7+9+11+13+15+17+19 is 100.