Is there a maths notation for "must be greater than"? I'm trying to say that in order for a given equation to hold true, x "has to be greater than" 5. Thanks, my maths is a bit rusty!
(Comment turned answer)
Suppose your equation in question is $f(x)=g(x)$. Then we may write $$(f(x)=g(x))\rightarrow (x>5)$$ which can be read as "$f(x)=g(x)$ implies that $x>5$". (You could add a universal quantifier saying "for all $x$ (blah)", but this is implied.)
Here's a little bit more information dealing with this in terms of propositional logic: Here the symbol $\rightarrow$ isn't just some denotation for "implies"; it actually has mathematical meaning. Given two propositions (things that are either true or false) $P$ and $Q$, the proposition $P\rightarrow Q$ is false only when $P$ is true and $Q$ is false, and true otherwise.
So writing $(f(x)=g(x))\rightarrow (x>5)$ means that we're claiming that it is true. As such, if $f(x)=g(x)$ is true, then it is necessarily the case that $x>5$ is also true.