The mathematical punchline is brilliantly nerdy! When you calculate sin(21°), you get approximately 0.3584... which is why 6 was scared of 7! Because 7 8 9 (seven ate nine)! 🤓
The joke works because sin(21°) equals cos(69°), which equals cos(789°) when you add 720° (which is just two full rotations around the unit circle, so mathematically equivalent). And cos(789°) sounds like "cuz 7 8 9" when read aloud!
It's the mathematical equivalent of a dad joke that requires a calculator and a degree in trigonometry! No wonder nobody's laughing - they're too busy checking the math! 🧮