   undo sine and cosine ???
  is there away to undo sine and cosinesin(5) = ~0.0871557how can you get 5 again?   
  arcsin(0.0871557) = 5or asin(0.0871557) = 5   ;  In general, you can't get the five back again since five lies outside the range for both arcsin and arccos. You can get a value that gives you the correct result when you apply sin or cos, but you won't necessarily be able to get back the exact same original input.   ;Quote:Original post by SiCraneIn general, you can't get the five back again since five lies outside the range for both arcsin and arccos. You can get a value that gives you the correct result when you apply sin or cos, but you won't necessarily be able to get back the exact same original input.Specifically, in this case, since sin(5) == sin(5 - 2π), there's no way to tell from "0.0871557" whether you meant 5 or 5- 2π.   ;  asin(sin(x))==x%2pi   ;  The range of asin is only -π/2 to π/2, so you won't get any results back that are in quadrants II or III.  You'll need additional information about the original angle, such as its cosine, to get something in the range 0 to 2π.  Even then, if the original angle was outside this range then there's really no way to determine the original period.And don't forget that the C/C++ math functions use radians, not degrees (sin(5°) = 0.08716).  A lot of other languages also use radians, a few might use degrees but I can't recall any off the top of my head.   