Question 15
For what value of $n$ is $$
\begin{aligned} &i + 2i^2 + 3i^3 + \cdots + ni^n \\ &= 48 + 49i? \end{aligned}
$$ Note: here $i = \sqrt{-1}.$
\begin{aligned} &i + 2i^2 + 3i^3 + \cdots + ni^n \\ &= 48 + 49i? \end{aligned}
$$ Note: here $i = \sqrt{-1}.$