What is 1 + 3 + 5 + 7 + 9 + 11 + ..... + (n*2) - 1, in terms of n?

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2^n
(n*(n+1)) * 3/2
4n
/sqrt{n}
n^2
n^4
(n*(n+1)) / 2
(n+1)(n-1)

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If you add both ends, you get 2n. Keep adding both ends and the sum will be 2n each time. You do this n/2 times. 2n*n/2 = n^2.