Return the result rounded to two decimals.

Why are you using trunc?

Also, check the note, just in case you're using another value of Pi.

put these at the beginning of your code:

print("-->" + form_ + "<--")

print("-->" + txt + "<--")

this way you can see the inputs

what language are you using?

errors are not random. you're trying to access data from a non-existant index of some container. the error message probably directs you to the line in your code where you made this mistake. try printing the inputs to see what you're dealing with

n = 2m+1 holds for negative n just as for positive n. So,

they should have the same odd order

No.

31 or -31?