Translation of "Justified" in Japanese

But an operation could also be justified.

手術を正当化することもできました

You are quite justified in answering him back.

君が彼に口答えするのももっともだ。

The boy more than justified the favourable opinion they had formed of him.

その少年は、彼らが彼を信用したのが間違いでなかったことを十二分に証明した。