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Understanding square roots

Learn how square root means what number multiplied by itself will result in the given number. Created by Sal Khan and Monterey Institute for Technology and Education.

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Video transcript

We're asked to find the square root of 100. Let me write this down bigger. So the square root is this big check-looking thing. The square root of 100. When you see it like this, this means the positive square root. If you're familiar with negative numbers, you know that there's also a negative square root, but when you just see this symbol, that means the positive square root. So let's think about what this is saying. This is asking us find the number, the positive number, that when I multiply that number by itself, I get 100. So what number when I multiply it by itself do I get 100? Well, let's see, if I multiply 9 by itself, that's only going to be 81. If I multiply 10 by itself, that is 100. So this is equal to-- and let me write it this way. Normally, you could skip this step. But you could write this as the square root of-- and instead of 100, 100 is the same thing as 10 times 10. And then you know, the square root of something times itself, that's just going to be that something. This is just equal to 10. So the square root of 100 is 10. Or another way you could write, I guess, this same truth is that 10 squared, which is equal to 10 times 10, is equal to 100.