# Day 5-Notes on Preprocessing Dataset

Fourier Transform: back to basics Why do we need negative frequencies and what is the meaning of a negative frequency in the first place? notes from answer on Quora Negative frequencies do not exist in reality. They are constructs in our heads. The idea behind it is actually very simple. Mr. Fourier said that any signal is composed of the superposition of sinusoidals with different frequencies. Mr. Euler said that a $2sin(2 \pi f.t) = e^{2i ft} + e^{-2i ft}$; $i= \sqrt(-1)$ In other words...