Question

find the sum of the series given below S=1+(1+2)+(1+2+3)+(1+2+3...n)​

Answer 1

Explanation:

n th term of the series is n(n+1)/2 ...

now sigma of this while n ranges from 1 to n

sigma of n²/2 + n/2

n(n+1)(2n+1)/12 + n(n+1)/2

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