Я люблю книги, у которых крепкий переплёт и аккуратный корешок.

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Breakdown of Я люблю книги, у которых крепкий переплёт и аккуратный корешок.

• книга: the book
• и: and
• любить: to like

Questions & Answers about Я люблю книги, у которых крепкий переплёт и аккуратный корешок.

Why is it книги here, and what case is it?

Книги is the accusative plural of книга.

The verb любить normally takes a direct object in the accusative case:

• Я люблю книгу = I love a book
• Я люблю книги = I love books

For inanimate plural nouns like книги, the accusative plural looks the same as the nominative plural.

Why does Russian use у которых instead of just которые?

Because Russian is expressing the idea books that have... by using the structure у кого/чего есть... or, in a relative clause, у которых...

Literally, книги, у которых крепкий переплёт... is something like:

• books, by which there is a sturdy binding...

But in natural English, that means:

• books that have a sturdy binding...

If you said книги, которые крепкий переплёт..., that would be ungrammatical. The relative pronoun needs to fit the structure of the clause, and here the clause is built with у.

What case is которых, and why?