Quote:
arc cosine is the inverse function of cosine

In the appropriate definition domains ;) For instance : [0, PI] for cos and [-1,1] for acos.

(I lost so many points in analysis as a student for not precising the restrictions of the functions on a definition domain f -> fd )

Even though your your question is probably answered:

I learned about acos when looking at a cosine table. I knew cos would take the angle and give me the ratio, but I had the ratio and needed the angle. My teacher informed me what I wanted was acos. Hopefully I didnt get that backwards.

Quote:Original post by Witchcraven
Even though your your question is probably answered:

I learned about acos when looking at a cosine table. I knew cos would take the angle and give me the ratio, but I had the ratio and needed the angle. My teacher informed me what I wanted was acos. Hopefully I didnt get that backwards.

Ah, thank you for pointig this out. I undstood what acos did (or at least the button for it on my calc ;)), but as I don't really know what cos does it doesn't mean much. You say cos gives you the ratio, the ratio of what?
Tera_Dragon

The basic trig functions give you ratios of the sides of right triangles from an angle in the triangle.

Sin(angle) = opposite/hypotnuese
Cos(angle) = adjacent/hypotnuese
Tan(angle) = opposite/adjacent

The inverted ones:

Asin(opposite/hypotnuese) = angle
Acos(adjacent/hypotnuese) = angle
Atan(opposite/adjacent) = angle

For example, tan(45 degrees) = 1.0 (I think). It's 1.0 because the opp/adjacent sides are the same length when that triangle is using a 45 degree angle.

The functions can be used to scale triangle and a whole bunch of useful crap, like rotating stuff an trajectories.

Hopefully I didnt explain a bunch you already know. Even more hopefully, I got all that right.

I remember doing that a year or so ago now. Thanks all the same.