Sunday, 7 January 2018

trigonometry - Why do both sine and cosine exist?

Cosine is just a change in the argument of sine, and vice versa.



$$\sin(x+\pi/2)=\cos(x)$$
$$\cos(x-\pi/2)=\sin(x)$$




So why do we have both of them? Do they both exist simply for convenience in defining the other trig functions?

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