He made up his mind not to say a word.

他打定主意一句话也不说。

He made up his mind to enjoy his guitar and to accumulate as many happy experiences as he could so that when he retired he would be able to look back on his life with satisfaction.

他下决心享受弹奏吉他，积累尽可能多的愉快经历，这样当他退休时，他将能够满意地回顾他的生活。

Once he made up his mind to do something, there was no stopping him.

他一旦下定决心做什么事，没有什么可以阻止他。

He had already made up his mind before even hearing her side of the story.

他甚至在听到她那一方的说法之前就已下定决心了。

"He's made up his mind to make friends with thee," replied Ben.

“他已经决定和你做朋友了。” 本回答说。