"The books are yours."

Translation: Cărțile sunt ale tale.

[brinkerl]

Why is "Cărțile sunt al tău." not acceptable?

[Romanian35]

because "ale tale" is the plural version."al tau" would be used if the noun was masculine singular. (ale tale is for feminine plural words) take a look at the website "learnromanian.com" for a chart on possessives