So I have this problem. I've got a_{n}=a_{1}+2(n-1) but in the answer they have a_{n}=n(n-1) And I'm kind of confused.
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according to the recursive formula $\displaystyle a_{n+1}-a_n=2n$ $\displaystyle a_n-a_{n-1}=2(n-1)$ $\displaystyle a_{n-1}-a_{n-2}=2(n-2)$ etc. so $\displaystyle a_n-a_1=2(n-1)$ is not correct
Originally Posted by nyanyona So I have this problem. I've got a_{n}=a_{1}+2(n-1) but in the answer they have a_{n}=n(n-1) And I'm kind of confused. Look HERE for the solution.
$a_{n+1} = a_n+2n$ $\begin{matrix} 1 & 2 & 3 & 4 & 5& ... &n\\ 0 & 2 & 6 & 12 & 20 & ...\\ 0\cdot1&1\cdot2&2\cdot3&3\cdot4&4\cdot5&...&(n-1)n \end{matrix}$
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