Arcsin in Valentin Albillo's HP-12C Tried & Tricky Trigonometrics

[jklsadf]

Yes that's it. Now that I look at it again, lines 61 to 66 are just using the identity asin(x) = atan(x / sqrt(1 - x^2)), where the scaled x^2 is stored in register 5, since the square root on line 52 isn't applied to register 5 in the last iteration, but its value is on the stack for the divide on line 64.

I got confused keeping track of stuff with the instructions in between. Line 59 has to be factorial (or could've been e^x or 10^x) to keep from having an extra 0 on the stack.

As far as I can tell, the only reason for doing the change of variable and using the arctan series instead of arcsin is the series is much simpler and thus fewer program steps. More advanced RPN programmables could've even combined lines 05 through 21 with lines 66 through 81 since they're very similar series, but the 12C doesn't have flags or subroutines.