This is the first edition of my book, you can find the expanded second edition here! Would you believe that today's most sophisticated wireless communications systems are based on the geometry and trigonometry taught in high school? It's true! This book applies basic geometry and trigonometry to complex numbers to establish a proper mathematical foundation for a successful DSP career.This book answers the following questions and many are complex numbers used in DSP?Why does Euler's formula use cosine and sine?Why are Cartesian form and Polar form complex numbers needed?Why does geometry and trigonometry apply to complex numbers?Why are radians used for angles?The book also includes simple derivations Euler's formulaTaking the derivative of cosine and sineProving the phase relationship between cosine and sine