The sum of n term of a series is n^2+2n for all value of n.find the first three terms of the series
The "sum of the first 1 term" is the first term. So substituting n=1 in n2+2n, gives 12+2(1) = 1+2 = 3.
So the first term is 3.
The sum of the first 2 terms is found by substituting n=2 in n2+2n, which gives 22+2(2) = 4+4 = 8. Since
the "sum of the first 1 term" is 3, the second term is 8-3=5.
The sum of the first 3 terms is found by substituting n=3 in n2+2n, which gives 32+2(3) = 9+6 = 15. Since
the sum of the first 2 terms is 8, the second term is 15-8=7.
In fact the sequence is the odd numbers beginning with 3,
3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,...
Edwin
