¡Hola! Since 'obra' (theater play) is a feminine noun, it will require a feminine adjective--'divertida' (fun), in this case. An easy gender/number matrix I use in my lessons is the following: gato negro (masculine singular) gatos negros (masculine plural) casa blanca (feminine singular) casas blancas (feminine plural) This matrix can be used to build upon in other considerations, such as: el gato negro (the black cat) los gatos negros (the black cats) la casa blanca (the white house) las casas blancas (the white houses) and este gato (this cat) estos gatos (these cats) esta casa (this house) estas casas (these houses) In any case, 'obra divertida' is like 'casa blanca'--feminine singular.

In spanish we put a gender to the sustantives (masculine and feminine), With this we can know how to add some other terms like emotions, verbs, etc. The words that ends with -L, -O, -N, -E, -R, -S are in general masculine, the others are feminine Your example: La OBRA de teatro que vimos anoche fue muy divertida. The sustantive is OBRA, it ends with A, so "Obra" is feminine, that's why we say divertidA and not divertido. If we say, the theater is very fun, "THEATER" is masculine, so we say it this way: El Teatro es muy divertido.

Hi! This is because 'obra' in Spanish is feminin -> 'la obra'. So, we have also feminin and masculine for the adjective, divertido or divertida, according to the noun. They always match in number & gender. Best regards, Alejo. REF.: I'm a Certified Spanish Teacher