Is the ideal $(X^2-3)$ proper in $\mathbb{F}[[X]]$? 
Let $\mathbb{F}$ be a field and $R=\mathbb{F}[[X]]$ be the ring of formal power series over $\mathbb{F}$. Is the ideal $(X^2-3)$ proper in $R$? Does the answer depend upon $\mathbb{F}$?

Clearly $X^2-3=(X+\sqrt3)(X-\sqrt3)$ and hence $X^2-3$ is not zero.
I have no idea whether the ideal is proper or not. 
So far, I didn't learn any theorem to prove an ideal is proper. Perhaps I should start with definition of proper ideal? Find one element in $R$ but not in the ideal ?

The element $\sum _{i \geq 0}  a_i X^i \in R$ is invertible in $R$ if and only if $a_0\neq 0$.
The key to the proof of that relatively easy result is the identity $(1-X)^{-1}=\sum_{i \geq 0}  1. X^i \in R $
In your question $a_0=-3$ so that the element $X^2-3$ is invertible in $R=F[[X]]$ (which is equivalent to the ideal $(X^2-3)\subset R$ being proper) if and only if the characteristic of the field $F$ is not $3$:   $$  (X^2-3)\subset R \;\text {proper} \iff \operatorname{char} F\neq 3.$$ 
