13) \( \sqrt{441}=21 \)

Did you know that the number 441 has quite a historical significance? It was once the postal code for St. John’s in Newfoundland, Canada, and is also interestingly noted in various cultural references, including as the name of a gear on the historic British steam locomotive, the "Flying Scotsman"! When it comes to square roots, a common mistake is forgetting that a square root can be both positive and negative. While we typically focus on the principal square root (the positive one), it's important to remember that both \(21\) and \(-21\) are technically correct when solving equations involving square roots like this one!