Grade 12th passAlgebra
Fin sum of n terms of the series 1+4+11+26+57+120... ... . ..... ...
Fin sum of n terms of the series 1+4+11+26+57+120... ... . ..... ...
1 Answer
Chetan Jain
The series is going in this way {(1-1)(2)+1}+{(2-1)(2)+2}+{(3-1)(2)+3}+..... Upto nth term,n means term no.
So nth term is {(n-1)(2)+n}=3n-2
So sum upto n terms = summation of 3n-2,n=1 to n
∑3n-∑2 where n=1 to n
=3∑n-2n
{3.(n)(n+1)/2} -2n
I hope you will understand
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