# How do you know if y=3x+2 is a function?

$y = 3 x + 2$ is not a function. Rather, it is just a regular linear equation. However, $f \left(x\right) = 3 x + 2$ is a function, because it contains "$f \left(x\right)$."
So, in general, if it contains "$y$," then you are safe in assuming that it is an equation. If it contains "$f \left(x\right)$," then you are safe in assuming that it is a function.