Geometric proof of derivatives of simple trig functions
I found this geometric reasoning (or proof) of a derivative of a Tangent function in Tristan Needham’s book on Visual Differential Geometry and it struck me as something really intuitive, simple and beautiful. I wanted to do similar derivations for other simple trigonometric functions, namely, Sine and Cosine of an angle. Although I was able to get the answers, it was not that succint or elegant as the proof of the Tan function....