Human: I have a question about the History of mathematical thought. Why did the ancient Greeks use the symbol <unk> for the square root of 2? Assistant: 
The symbol <unk> was used because the Greeks thought that the square root of 2 was a sacred number. The Greeks believed that the square root of 2 was the number that was the most perfect and complete. The square root of 2 was also known as the golden ratio, and the Greeks believed that the golden ratio was the most beautiful and perfect ratio.