When I want to refer to an equation similar to this image, what term should I use? Is it correct to say "Equation 3", although the equation contains a proportionality symbol?
closed as unclear what you're asking by FumbleFingers, Nathan Tuggy, joiedevivre, Michael Rybkin, Varun Nair May 7 '18 at 7:06
Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.
Yes, you can use equation when you reference this expression.
According to Wikipedia, an equation is always a statement of equality. Equality is an example a relation. Inequality, another relation, has the separate term inequation for a statement that describes it - but that term is somewhat uncommon (it is a dictionary word but my spell checker is unaware if it).
For the proportionality relation you can use the word proportion.
Other relations, such as congruence, membership, inclusion, or orthogonality, don't have specific names for statements describing them.
However, in technical writing, an equation is a part of the text that describes a statement in symbolic language, often with a label that can be used for reference (such as "equation 1-32"). The statement can be about any relation between things, not necessarily equality. It can also describe inequality, congruence, proportionality, membership, inclusion, orthogonality, and other relations.
If you want to be specific about the kind of relation you can also refer to it with more specific terms. For example, the Triangle inequality can be written as
||x|| + ||y|| > ||x + y|| (1-32)
And then you can refer to it as Equation (1-32) but also as Inequation (1-32). Note however that most technical writing tools will enforce using the same term in cross references - so I would say using "inqeuation" in technical text is rare.