English adjectives are less radical than Portuguese adjectives. In Portuguese, the gender and number (singular or plural) of all adjectives must always agree with the accompanying noun. This means that a masculine noun must always be accompanied by an appropriate masculine adjective and feminine noun by an appropriate feminine adjective. For example:

a new car = um carro novo
two new cars = dois carros novos.

Forming Feminine Adjectives

Forming Plural Adjectives