I remember wondering what these strange "sin" and "cos" functions were in Delphi 2 or something – it was ~1997 and I couldn’t just google it – and tried to find a pattern in the seemingly arbitrary output values. I don’t think trying to plot them as y=f(x) crossed my mind, not at first anyway, but instead I somehow ended up trying to plot x=k sin(t), y=k cos(t) and was amazed when I realized that they traced a circle on the screen. Only later I learned in school that they had anything to do with triangles. To me they were functions for emitting circle coordinates first and foremost.