Essentials Of Swedish Grammar -
Röda bilar (red cars)—the adjective typically ends in -a .
Adjectives must agree with the noun they modify in both gender and number. En röd bil (a red car). Essentials of Swedish Grammar
For more in-depth study, the Essentials of Swedish Grammar by Åke Viberg is a widely recommended practical guide. Röda bilar (red cars)—the adjective typically ends in -a