√49 equals?

• A. -7
• B. 7
• C. 49
• D. 0

Answer: (B)

The main idea is knowing what the square root means: the principal square root is the nonnegative number that, when multiplied by itself, gives the number inside the radical. For 49, which number times itself equals 49? 7 × 7 = 49, so the square root is 7. The negative number -7 also squares to 49, but the symbol √ denotes the nonnegative root, so it picks 7. The other numbers don’t fit: 49 would give 49^2, not 49; 0 gives 0 when squared.