# How to determine if given “complex” time complexity is $O(n^2)$?

If a given time complexity, such as these:

1. $$(n + \log n) * \sqrt{n+\log n}$$
2. $$n * (200 + \log^2 n)$$
3. $$(7+n^3)\log(n^5)$$

is not determinable by just looking at it whether is it in class $$O(n^2)$$ or not, how do I decide? If a time complexity is given, and in it there are more types of expressions (exponential, logarithmic, polinomial, … ) how do I decide which one determines the $$O(n^2)$$ or $$O(n\log n)$$ or … complexity?