Like cos(, the result of cosֿ¹( depends on whether the calculator is in Radian or Degree mode. However, unlike cosine, the result is in degrees or radians, not the argument. A full rotation around a circle is 2π radians, which is equal to 360°. The conversion of θ=cosֿ¹(n) from radians to degrees is θ*180/π and from degrees to radians is θ*π/180. The cosֿ¹( command also works on a list.
The cosֿ¹( function can be defined for all real and complex numbers, but assumes real values only in the closed interval [-1,1]. Because Z80 calculators have their trigonometric functions and inverses restricted only to real values, the calculator will throw ERR:DOMAIN if the argument is outside of this interval, no matter what the mode setting may be.
Since the function cosine itself doesn't have the restrictions that arccosine does, and since arccosine is the inverse of cosine, you can use cosֿ¹(cos( to keep a variable within a certain range (most useful for the home screen). Here is an example for a game like pong. The ball travels between 0 and 12.
You could use a flag like this:
:If X=12 or not(X \\ X is the position :-D→D \\ D is the direction :X+D→X \\ new position :Output(8,X,"=
An easier way to do this, without needing a flag or even an If statement, is using cosֿ¹(cos(
:X+1→X \\ Note: the calculator is in Degree mode :Output(8,cosֿ¹(cos(15X))/15,"=") \\ I used 15 because cosֿ¹ ranges from [0,180] and X from [0,12], so 180/12=15
- ERR:DOMAIN is thrown if you supplied an argument outside the interval [-1,1]
- ERR:DATA TYPE is thrown if you input a complex value or a matrix.