This may not be useful and I’m not exactly sure what you’re trying to ask but I’ll do my best to explain.
For the square root of 48, you can simplify it by finding two numbers; one of them having a perfect square and whatever number you choose for the second one, you find numbers there with one number having a perfect square. So for example, I would do 4*12 since it’s the easiest one I know. 4 has a square root of 2. However, with twelve, you can find two numbers that multiply to it with one of them with a perfect square, which would be 4*3,(again 4 having a perfect square root). So you would multiply 2 from the first 4(when you square rooted it), and the second 2( from 4*3). You should get 4 √ 3. The little sign means square root by the way. And if u wanna make sure they are equivalent, you can find the square root of 48 and find the product of 4 times the square root of 3. They should give the same answer.
You cannot simplify the square root of 15 as there are no two numbers with one of them having a perfect square.
You can simplify the square root of 100, that gives you 10.
This may not have helped, but I tired to explain it the best I could. Let me know if u want another explanation :)