happy的形容词形式是本身，happy。

adj.感到(或显得)快乐的;高兴的;给予(或带来)快乐的;使人高兴的;幸福的;表示祝愿，如Happy Birthday生日快乐、Happy New Year新年好等

例句：

I said I'd go, just to keep him happy.

我说过我要去只是为了让他高兴。

Every time I hear that song I feel happy.

我每次听到那首歌都感到很愉快。

The bank is happy to loan money to small businesses.

银行乐于贷款给小型企业。

She seems reasonably happy in her new job.

她在新的工作岗位上好像还挺开心。