Question

Sa se calculeze suma:
1 x+ 2 x²+ 3 x³+...+n xla puterea n

Answer 1

1x+2x²+3x³+...+nx$^{n}$⇔
$\frac{ x(x^{n-1}) }{ (x-1)^{2} } + \frac{ x^{(n+1)} }{(x-1)}$