• Most adjectives ending in -a or -o have four forms to agree with a noun if it's masculine (-o), feminine (-a), or plural (-os, -as): día largo, clase larga, días largos, clases largas.

• Adjectives ending in -sta or -ta are the same in the masculine and feminine (indígena also):
un hombre idealista, sociedades capitalistas, políticos demócratas, un texto indígena.

• Most adjectives ending in -e or a consonant are also the same in the masculine and feminine:
una profesora inteligente, un poema difícil, ensayos útiles, novelas importantes.

• A small group of adjectives ending in consonants do have separate feminine forms. The most common of these are adjectives of nationality and those ending in (-or): una estudiante alemana, ciudades inglesas, mujer trabajadora.

• The adjectives bueno and malo are shortened to buen and mal before masculine singular nouns:
un buen amigo, un mal día (but: buenos amigos, malos días).

• Grande shortens to gran before a singular noun, masculine or feminine:
un gran país, una gran mujer (but: grandes países, grandes mujeres).