Mdtryhht

I am learning uses of articles.

And the book i am using tells that

"article the is used when a singular noun is meant to represent a whole class"

For example
The cow is a useful animal.

I want to know the reason how the above example represents a class.
How can I prove it represents a whole class

This question seems foolish but I am really confused please help me

And correct me where I am wrong

Class literally just refers to groups. In that example, it’s equivalent to saying “Cows are useful animals.” For instance, “The dog is man’s best friend.” Here you’re not talking about a particular dog, but dogs in general. You can also say “The cook must taste what he cooks.” Cook here refers to all cooks.

However, “the” does have another meaning and it’s important not to confuse the two. The other meaning also acts like an article, but refers to a specific object. “The cow is dead.” Cow here does not refer to all cows, but a particular cow (maybe in front of you or something). This is to refer to something that’s has already been mentioned before, or that you’re already pointing at it. “The” here is synonymous to “that”.

The construction you ask about is called a Generic noun phrase; this kind is a Definite Generic.

You should know, however, that there is no single rule for use of articles. Instead, there are hundreds of individual rules for special cases, particular noun phrases, idioms, and syntactic constructions like this one. And each case has to be recognized and memorized separately, because they don't correlate with one another.

The and a/an are just markers, like flags of one color or another, that indicate specific usages and don't have any meaning themselves. Asking how to use the is like asking how to use the color red; there aren't any general rules, only specific ones, and everything depends on the context.