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Comment: Added some trivial examples.

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Added domain and range (for real numbers).

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Domain: 1 <= x <= 1 Range: 0 <= y <= Pi 
DRAFT 
SDL_acos
Use this function to compute arc cosine of x.
Contents
Syntax
double SDL_acos(double x)
Function Parameters
x 
floating point value, in radians. 
Return Value
Returns arc cosine of x.
Code Examples
/* acos(x) = Pi/2  asin(x) */
SDL_Log("acos(0):\t\t%f", SDL_acos(0));
SDL_Log("Pi/2  asin(0):\t%f\n", M_PI / 2  SDL_asin(0));
/* acos(x) = Pi  acos(x) */
SDL_Log("acos((1)):\t%f", SDL_acos((1)));
SDL_Log("Pi  acos(1):\t%f\n", M_PI  SDL_acos(1));
Remarks
The definition of y = acos(x) is x = cos(y). Domain: 1 <= x <= 1 Range: 0 <= y <= Pi
Version
This function is available in >= SDL 2.0.2.