3×9=?

At the very beginning, I was a bit stunned. How did the square root turn into a division sign and still yield the correct result? So, I picked up my pen and wrote down an equation... It turns out that as long as it's in the format of "N×N²=？", it works, for example, 2×4=？, 4×16=？, 5×25=？... At first glance, it seems quite magical, and I thought it might be some kind of divine skill that complicates things, but it turns out to just be a joke.