What is the square root of 81? (alternate phrasing)

• A. -9
• B. 9
• C. 3
• D. 81

Answer: (B)

Finding the square root means identifying the nonnegative number that, when multiplied by itself, equals the original number. Since 9 × 9 = 81, the square root of 81 is 9. The square root symbol denotes the principal (nonnegative) root, so we use the positive value. The number -9 also squares to 81, but the standard square root is the positive one. The other options don’t fit: 3 squared is 9, not 81; and 81 is not a square root of 81 (it’s the original number that结果 from squaring 9).