> 
> Find the sum of $1.2+2.3x+3.4x^2...\infty$ where $|x|<1$
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I have got the $\mathbb{n^{th}\quad term \quad= n(n+1)(x^{n-1})}$

Then I tried finding $\sum\limits\_{k=1}^\infty n(n+1)(x^{n-1})$ but it's in product form so couldn't.

How do I continue from here?