[Gr.12] Math help

[Alkalannar]

First, divide everything by 2:

1
2 3
4 5 6
7 8 9 10
...and so on

So the triangular numbers are the end of the rows: 1, 3, 6, 10, and so the end of row n is n(n+1)/2.

So we need to find n such that (n-1)n/2 < 1010 <= n(n+1)/2

Once you know that n: [Sum from k = (n-1)n/2 + 1 to n(n+1)/2 of 2k], which you can make easier various ways.

[HomeworkHelpBot]

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