Euler's formula

[Bin Shao]

1. After applying Euler's formula to

x(t) + iy(t) = \sum_i^N R_i(\cos(\omega_i t + \phi_i) + i\sin(\omega_i t + \phi_i))

I think it should be \sum_j^N R_je^{i(\omega_j t+ \phi_j)}.

In the index.html, it is

\sum_j^N R_je^{i\omega_j t+ \phi_j}

2. For \omega_j = \frac{2 \pi i j}{N}, i think it should be: \omega_j = \frac{2 \pi j}{N}