Could someone please explain why the Arduino produces different results?
Thank you
Isn't the real question, what happens with Atmel Studio on a naked 328P with all the latest packages?
The issue may just be with the AVR-GCC math library. Arduino does not package the latest version of AVR-GCC, so we could be looking at an already "fixed" issue.
Things like this can get under ones skin... When in college years ago, I was dismayed to find my TI scientific calculator would not answer 0 to sin(45) - cos(45) while the dude that sat across from me had an HP and it did give 0. Needless to say, my anal self sold the TI and bought an HP67... And never looked back!
Ray