In \(\displaystyle{6}{x}{<}{\left({x}+{9}\right)}\) the expressions \(\displaystyle{6}{x}{\quad\text{and}\quad}{\left({x}+{9}\right)}\) are joined with < inequality sign. It is obtained when an expression is related with another expression using the inequalities sign (\(\displaystyle{<},{>},\le,\ge\)).

That means, that \(\displaystyle{6}{x}{<}{\left({x}+{9}\right)}\) is an inequality.