Is is just me being a n00b or are there a few errors in the equations? Like the exponential definitions of sin and cos, a missing negative sign in proof of m≠n,

Is is just me being a n00b or are there a few errors in the equations? Like the exponential definitions of sin and cos, a missing negative sign in proof of m≠n, maybe more later not sure. Somewhat perplexing for someone learning the stuff BUT then again, I'm in medicine; so it might actually just be me. Relevant for other learners is the digital signal processing lectures on Coursera, highly recommended with python notebooks and quizzes. https://www.coursera.org/learn/dsp https://www.coursera.org/learn/dsp