你好、Chunweiさん。

> There are two types of adjectives in Japanese; i-adjectives and na-adjectives, and the predicative usage of i-adjective, which means when adjectives come at the end of the sentences, is;

dictionary form: 忙しい

present/future positive:  忙しいです(formal)

past positive:  忙しかったです(formal)

i-adjectives end in 'i' sound without consonants preceding them.

e.g. おいしい、うれしい、あつい　→　おいしかった、うれしかった、あつかった

> The dictionary form of verb shows both present and future positive tenses.

dictionary form:   疲れる

present and future positive:  疲れます(formal)

past positive:  疲れました(formal)

e.g. 食べる、行く、勉強する　→　食べました、行きました、勉強しました

I hope this helps.

再見！；D

Japanese Practice - 3 Sentences a Day #4