What is the square root of 64?

The square root of a number is defined as a value that, when multiplied by itself, gives the original number. In this case, the original number is 64. When we assess which number, when squared, results in 64, we find that 8 multiplied by 8 equals 64 (8 x 8 = 64). Therefore, the square root of 64 is 8.

The other options do not yield 64 when squared: 10 squared equals 100, 6 squared equals 36, and 9 squared equals 81. Thus, the correct choice, representing the value whose square produces 64, is 8.