Question

given a series of numbers find the sum of first n numbers. The series is 1, 3, 6, 10, 15, ....

Answer 1

a=1

d=2

Sn = n/2 (2a +(n-1) d)

Sn = n/2(2*1 +(n-1) 2)

= n/2(2+2n-2)

= n/2(2n)

=n^2

Your answer is n^2

Hope this helps you.

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