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very hard; with utmost effort; as hard as one can; with all one's might; for dear life; eagerly; desperately
一生懸命勉強して合格しました。
I studied hard and passed.
一生懸命働いて疲れました。
I worked hard and got tired.
一生懸命練習すれば上手くなります。
If you practice hard, you will improve.