égale vs égal

Égale is the conjugation of the verb Égaler in the context of mathematics.

Here, I honestly think they made a mistake with the writing and inflections because a math equation (a singular subject) requires a conjugation for it to make grammatical sense. 

Seng, 

colloquial French usage is as Aurélie has explained in the lesson. 

In everyday usage ‘ égal ‘ is regularly used in the simple ‘ translation ‘ of the mathematical equation, which is a series of mathematical symbols only, into words. Consider ‘ égal ‘ to be a shortened noun form - le signe égal - used as a descriptor of that symbol in the equation. 

This is why the first few examples are presented in that form.

However, you can use the verb form, ‘ égale ‘, grammatical agreement in the third person singular when writing the mathematical equation in words, if you wish.

 If you are expressing something more than the equation itself, a verb is necessary, and using ‘ égaler ‘ is an option eg ‘ la somme de deux et deux égale quatre ‘ ( agreement with the subject ‘ la somme ‘ ).

Of course, in speech it is an unheard difference between égal and égale, and it is not all that often you will need to be writing mathematical equations in words rather than numbers and symbols ! 

I agree with Joseph, and this article, which discusses whether it should be égale or égalent, but has no doubt that it should not be an adjective.

https://www.lemonde.fr/blog/correcteurs/2014/01/21/zero-plus-zero-egale-la-tete-a-toto/

Alan, 

I am sure you read below the link and found not everyone is in agreement, and this debate extends back centuries. 

It will not be resolved here, but a mathematical equation does not contain nouns, verb or adjectives. 

If putting 'into words' the mathematical equation there is no subject, no verb, no object. 

If making a sentence, you can consider grammar, but there is still not complete agreement evidently. 

I have checked with my circle of French contacts - maybe it is regional, maybe it is generational, but they agree with what is presented here in the lesson as Aurélie has written it. 

It is not worth wasting more time on, as both are accepatble,  and in fact, if you want to reference Robert, you can even include ' égalent " as being acceptable. 

The answer to the original post remains the same.

https://dictionnaire.lerobert.com/definition/egaler