What do [] mean and what does it mean if it is used in an equation?

What do the square bracket symbols mean? Are they what I hear are "sets"? And when it is in an equation, how is it interpreted?

Here is an example:

$$\dfrac{dy}{dx}[2x^{2}+y(x)^{2}]=50x+2y(dy/dx)=0$$

1 Answer

Sometimes they are the same as parentheses. Like in $\sum \left[ f(n) - g(n) \right]$ or the expected value $\text{E} \left[ X \right]$. They may have different meanings if they are specially defined.

Or if you meant $\{ \}$ then these are braces and yes they are often used to represent sets.

There is a lot of ambiguity in the proper nomenclature.