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Geometric Progression 



Problem 15 of 23 


15. 1 + (1 + 3) + (1 + 3 + 5) + ... n terms










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Geometric Progression 
15. 1 + (1 + 3) + (1 + 3 + 5) + ... n terms
`S_n = sum [ f(n) ]`
`= sum [ sum (2n  1) ]`
`= sum [ 2 sum n  sum 1 ]`
`= sum [ 2 * (n (n + 1))/2  n ]`
`= sum [ n^2 + n  n ]`
`= sum n^2`
`= (n (n + 1) (2n + 1))/6`





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