# How do you evaluate function notation?

In fuction notation, you have a variable (often the function $f$) which values depends on those of another variable (often the indipendent variable $x$).
When we write something like $f \left(x\right) = {x}^{2} - 3 x + 2$, we mean that for every number $x$, we must behave in the same way to evaluate $f$: in this case, we must sum the square of that number, then subtract its triple, and then add 2.
Evaluating a function simply means to substitute the exact value in the generic expression of the function. In my example, if you want to calculate $f \left(5\right)$, you simply need to replace every $x$ with a "5", and so
${x}^{2} - 3 x + 2 \setminus \rightarrow {\left(2\right)}^{2} - 3 \setminus \cdot 2 + 2 = 4 - 6 + 2 = 0$