In italian, the article in front of possessive pronouns is sometimes optional, but it is never a mistake.
• "Le forchette sono tue" = "Le forchette sono le tue"
The difference is Very subtle and IMHO there is no real difference in meaning
instead, there is a slight difference in meaning if the sentence is in its negative form.
• "Le forchette non sono tue" = "the forks are not yours" (maybe you have some forks or maybe you don't have any).
• "Le forchette non sono le tue" = "the forks are not yours" (but surely you have or you have had some forks)
Sono is the right verb. 'Tu' is not the subject, 'tue' is the possesive pronoun; the forks are the subject. In the English sentence you say 'the forks are yours' not because it's 'you are' but because forks are plural. Similarily, you could say 'the forks are mine' , not 'the forks am mine'
Pronouns (like tue/tuo), adjectives (like nero) and determiners (like le) must agree on gender and number with the noun. Forchett
e is feminine and
plural (of forchetta). A masculine example is coltello (
- (tuo coltello) Il coltello è il tuo = (your knife) The knife is yours
i= (your knive
s) The knive
- (tua forchetta) La forchetta è la tua = (your fork) The fork is yours
e= (your fork
s) The fork