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I guess just triangles. I was just wondering because [itex]\cos[/itex] seems to be the only one that will change if it's [itex]\cos^{-1}[/itex] to a different number.Data said:Not at all.

Have you seen trigonometric functions defined using the unit circle, or just triangles?

In general, [itex]\cos (-\theta) = \cos \theta[/itex], though, so [itex]\cos^{-1} (-x) \neq \cos^{-1} x[/itex].

I was just wondering what made it change like that, while [itex]sin[/itex] and [itex]tan[/itex] don't.