(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Find a general formula for

[tex] (1\cdot 2) +(2\cdot 3) +... + (n\cdot (n+1)) [/tex]

2. Relevant equations

The sum of the first n integers

[tex] 1+2+3+... + n = \frac{n(n+1)}{2} [/tex]

3. The attempt at a solution

i thought of doing this

[tex] (1+2+3...) * (2+3+4+...) [/tex]

but then the problem of cross terms comes about

additionally this is not an arithmetic series nor a geometric series because the common difference increases by 1 each term and there is no common factor.

how wouldi get rido of the cross terms??

do i even need to do it this way?? Another method is possible??

Please help!!

thanks!

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# Homework Help: Sum of a series

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