Find the sum `2+5+10+17+26+. . . .`

Explanation

Assume, ` T_{n}` be the nth term


`S_{n}` be the sum to n terms of series.


`S_{n}=2+5+10+17+26+ldots ldots ldots ldots+{T}_{{n}-1}+{T}_{{n}} ldots(1)`


Equation (1) can be write as:


`S_{n}=2+5+10+17+26+ldots ldots ldots ldots .+T_{n-1}+T_{n} ldots(2)`


Subtract equation (2) from (1),


`S_{n}=2+5+10+17+26+ldots ldots ldots ldots+T_{n-1}+T_{n}`


`S_{n}=2+5+10+17+26+ldots ldots ldots ldots+T_{n-1}+T_{n}`


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