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I don't have any formal education in Trigonometry or Calculus, but I'm studying a book on Pre-calc before school begins this fall. I've completed College level Algebra too, so math isn't something which I have a whole lot of trouble with.

I'm actually working on a game in Unity3d, and I picked up the pre-calc book because I need to understand more about rotations, and vectors, and such, additionally I'm taking Pre-calc at a University this fall. I don't think I've run across an answer to this question yet in the book, if I didn't miss it or it hasn't yet been introduced.

For some problems in this game essentially I need to find the angle between a point an some origin in space. The question is: does the trig function I need to use depend on which quadrant the point is in?

I ponder the answer to this because it matters what angle you are computing when you decide on inputs for the trig functions.

[edit] is this much clearer, or no?

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  • $\begingroup$ Your real question doesn't seem to be quite clear right now. $\endgroup$
    – Daniel W. Farlow
    Commented Jul 2, 2015 at 17:27
  • $\begingroup$ Ok I will try to clarify $\endgroup$
    – MegaWitt
    Commented Jul 2, 2015 at 17:27

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In 2D, you don't need to use different trig functions, its pretty much the same sin, cos, and tan you'd always use, but the sign (plus or minus) of the trig functions do change depending on what quadrant you are in. A good way to remember when a trig function is positive or negative is to use the acronym "All Students Take Calculus". To see this in action, just draw a coordinate plane (a unit circle more specifically) and put the first letters of each word in the acronym with the corresponding quadrant (ex. A in 1st quad, S in 2nd quad, and so on). Each of the first letters in the acronym helps you remember the sign of the trig functions, as seen in the picture bellow. (ignore the angles and picture to the top right)

enter image description here

However, I you are referring to 3D coordinates it is a little more complicated. You can check out this other related question I answered that deals with angles and programming.

Coordinate calculation on a unit sphere

Hope this helps

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  • $\begingroup$ More than helpful! I did need to know about 3d rotations too at some point =D $\endgroup$
    – MegaWitt
    Commented Jul 2, 2015 at 18:07

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